Legal Explanation

The Estoppel Doctrine plays a significant role in patent infringement litigation in China. It entails that if a patent holder narrows the scope of their claims, such as through restrictive amendments or interpretations, during the patent prosecution process, including examination of patent applications or subsequent procedures like invalidation, opposition, or reexamination, in order to meet the statutory requirements for the patent grant, they cannot later assert that the subject matter abandoned through such narrowing falls within the scope of patent rights.

Conditions for the Application of Estoppel Doctrine

In Chinese judicial practice, the application of estoppel doctrine generally necessitates the fulfillment of the following conditions:

(1) Explicit and recorded restrictive amendments or abandonment of technical solutions must be present in the patent documents.

(2) If CNIPA or the IP courts have indicated expressly during the patent examination or validation that the patentee's restrictive amendments or abandonment of the technical solution are insufficient to overcome substantial defects in the original claim, applying the estoppel doctrine in infringement litigation may be hindered.

(3) The estoppel doctrine limits the application of the doctrine of equivalents. When the doctrine of equivalents is established, considering estoppel is unnecessary. The estoppel doctrine comes into play only when the doctrine of equivalents is not established, and infringement needs to be determined based on the doctrine of equivalents.

(4) Applying the estoppel doctrine requires a request from the alleged infringer and the provision of evidence by the alleged infringer regarding the patentee's change of position. The court does not actively introduce evidence or apply the estoppel doctrine but may investigate and verify relevant evidence through administrative agencies upon the parties' request.

Case study

In order to illustrate situations involving the abandonment of technical solutions, restrictive amendments, and explicit denied statements of opinion, we will examine three patent litigation cases.

1. Abandonment of technical solution

Case Number: (2013) Gao Min Zhong Zi No. 362

Patent Number: CN100588049C

In this case, the central issue revolves around a specific feature: "The data terminal is situated on the upper side of the outer wall of the insulating body, while the power terminal is positioned on the lower side of the inner wall of the insulating body." However, the accused infringing plug has both the power and data terminals on the "inner wall." The patentee asserts that this constitutes equivalent infringement.

The accused infringer invokes the estoppel doctrine, contending that the patentee completely removed the technical solution outlined in claim 2 (which involved both terminals being located on the inner wall) during the application process. Furthermore, the patentee acknowledged in their arguments that claim 2 lacked inventive steps, as pointed out by the examiner. Consequently, the patentee explicitly abandoned the technical feature of "both the power terminal and the data terminal located on the inner wall," deeming it a non-substantial improvement over the prior art. Based on the principles of the estoppel doctrine, the patentee's abandonment of this technical feature during the application process implies that it should not be encompassed within the scope of patent protection.

Both the first-instance and second-instance courts concurred with the accused infringer's claim of estoppel doctrine, ruling that the accused infringer did not violate the patent.

2. Restrictive amendments

Case Number: (2005) Gao Min Zhong Zi No. 1262

Involved Patent: CN1130063C

In this case, the focal point is a specific feature: "Detecting and comparing the current user card's corresponding mobile number with the pre-stored mobile number corresponding to a legitimate user card. If they match, normal usage is allowed; if they do not match, normal usage is allowed while automatically making a hidden call according to the set functional parameters." Based on this feature, the patentee alleges infringement under the doctrine of equivalents.

During the initial patent examination, the patentee explicitly stated: "In comparison, prior art 1 and 2 are designed to prevent unauthorized users from accessing, whereas the present invention is primarily intended for reporting loss. The present invention allows the current user to use it normally, but if the user is unauthorized, it initiates a loss reporting call without the user's awareness, thereby achieving the purpose of reporting the loss. The effect is significantly different." Consequently, the patentee abandoned the technical solution wherein unauthorized users could not use the device usually and made a visible call for reporting the loss. It was based on this amendment that the patent was granted.

In the final ruling, the Beijing High People's Court held that the patentee had abandoned the technical solution mentioned above during the initial examination to obtain the patent. Following the estoppel doctrine, when the court applies the doctrine of equivalents to determine the scope of patent protection, the patentee is precluded from reintroducing restricted, excluded, or abandoned content into the scope of patent protection.

As a result, the accused infringer was found not to have violated the patent.

3. Explicitly Denied Statement of Opinion

Case Number: (2017) Supreme People's Court Civil Application No. 1826

Involved patent: CN101000977B

This case involves essential features designated as a, b, and c (specific details not provided). During the substantive examination stage, the examiner explicitly rejected the applicant's statement of opinion regarding the inventiveness of features a and b. Consequently, the applicant supplemented feature c into Claim 1, and the patent was granted based on this amendment.

In the subsequent invalidation procedure, the patentee emphasized the inclusion of features a and b through a restrictive amendment. However, the Patent Reexamination Board did not specifically evaluate whether features a and b rendered the patent inventive. Instead, they based their determination solely on feature c, affirming its inventiveness and upholding the patent's validity.

The appellate court ruled that the Patent Reexamination Board's failure to conduct a specific evaluation of whether the distinguishing features a and b rendered the patent inventive did not meet the requirement of "explicit denial." Therefore, the estoppel doctrine should be applied in this case.

Upon retrial by the Supreme People's Court, it was concluded that the examiners did not recognize the patentee's statement of opinion regarding features a and b and held an explicitly denied opinion. The Patent Reexamination Board did not overturn the opinion reached during the substantive examination stage, and the invalidation procedure did not yield a contrary conclusion. Consequently, it is considered that the patentee's restrictive amendment did not result in the abandonment of the technical solution. Thus the estoppel doctrine should not be applied when determining infringement.

Countermeasures to be Taken

Based on the above cases, the following are briefly discussed as countermeasures that patentees should consider.

(I) Authorization Stage

Statement of Opinions: When responding to substantive examination opinions on novelty and inventiveness, it is advisable to address the deficiencies pointed out by the examiner without making statements on unrelated technical features. Suppose the examiner accepts the novelty and inventiveness of specific claims and intends to limit them as independent claims. In that case, it is recommended to provide only formal statements, refraining from substantive statements.

Careful Presentation of Opinions: When presenting statements of opinions regarding prior art, distinguishing technical features, technical problems, and technical effects, avoid intentionally exaggerating technical issues and effects to obtain authorization. This helps to prevent complications in applying the doctrine of equivalents during infringement proceedings.

Removal of Technical Solutions: If there is a need to remove a specific technical solution, direct abandonment or self-admission of lack of inventiveness should be avoided. When modifying a higher-level technical feature to a lower-level one, it is recommended to encompass as many technical solutions from the embodiments described in the specification as possible.

Proactive Submission of Supplementary Opinions: If an error is discovered in a previously submitted statement of opinion that may trigger the application of the estoppel doctrine during the examination process, it is permissible to submit supplementary statements of opinion to rectify the mistake proactively. Such proactive actions do not fall under the prohibition of changing one's position.

Rights Confirmation Stage

In invalidation proceedings, particularly those associated with patent infringement litigation, the invalidating party may attempt to invalidate all patent claims and induce the patentee to make interpretations and limitations favorable to the invalidating party. This can substantially restrict the scope of protection and lay the foundation for non-infringement defenses in subsequent patent infringement litigation.

Therefore, in invalidation proceedings, the patentee must seek the broadest possible scope of protection while avoiding excessive restrictive amendments to the claims. This helps prevent the estoppel doctrine's application, which could adversely affect future patent enforcement actions.

Patents within the Same Family, Divisional Applications, and Others

In addition to the examination document of the patent in question, the examination document of divisional applications may also impact the application of the estoppel doctrine in patent infringement litigation, as recognized by judicial interpretations of patent infringement. Furthermore, statements of opinion submitted during the substantive examination stage of patents within the same family, as well as the specifications of other related patents filed by the same applicant, can be utilized to interpret the claims of the patent in question according to the civil adjudication of the Supreme People's Court.

Therefore, it is essential to focus on modifications and statements of opinion related to the specific patent and pay attention to other patents connected through divisional applications, patents sharing a common priority, and similar patents filed by the same applicant. This ensures that unnecessary restrictive interpretations, which could affect the scope of protection and subsequent enforcement actions by the patentee, are avoided.


Through case studies, we provide insights into the application of the estoppel doctrine in Chinese patent litigation, highlighting considerations for patentees. Countermeasures include:

Providing focused statements of opinions during the authorization stage.

Avoiding exaggerated claims of technical problems.

Strategically handling the abandonment of technical solutions.

During rights confirmation, patentees should seek broad protection and avoid excessive restrictive amendments to prevent adverse effects on subsequent enforcement. Attention should also be given to related patents, including divisional applications and those from the same applicant, to ensure comprehensive protection and avoid unnecessary restrictive interpretations. By implementing these measures, patentees can navigate the estoppel doctrine effectively and protect their intellectual property rights.

Originally published 5 September 2023

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.