Parameter-defined claims in China: overview, challenges, and opportunities

Parameter-defined claims are a drafting technique that delineates the technical features of a product by reference to measurable physical or chemical parameters – such as melting point, molecular weight distribution, and crystal diffraction peaks – and are widely employed in the fields of chemistry, materials science, biotechnology, and new energy batteries. Sections 3.2.2 (Part II, Chapter 2) and 4.3 (Part II, Chapter 10) of China’s Patent Examination Guidelines provide that where structural features alone are insufficient to clearly characterise a product, parameters may be used for this purpose.

Notably, different parameters carry varying degrees of distinguishing power in novelty assessments: parameters that directly imply a specific structural difference – such as X-ray diffraction peaks unique to a particular crystal form – possess stronger distinguishing power, whereas parameters reflecting only general performance attributes (e.g., thermal conductivity) may be presumed to be equally met by prior art products, thereby placing novelty at risk of rejection.

Sufficiency of disclosure (Patent Law, Article 26(3)) has increasingly become one of the most contested issues in invalidation proceedings. Three of China’s ten landmark re-examination and invalidation cases in 2023 involved this issue. The core rule is as follows: where a parametric formula is derived under specific conditions, the specification must provide experimental data in support; likewise, merely stating a target parameter without disclosing the concrete technical means for achieving it fails to satisfy the sufficiency of disclosure requirement.

Clarity and support (Article 26(4)) require that the measurement conditions for the parameters be clearly and reliably specified, and that the parametric scope covered by the claims be adequately supported by the working examples in the specification.

Regarding novelty and inventive step, the Patent Examination Guidelines establish a presumption rule: where the claimed product cannot be distinguished from a prior art product on the basis of the parameters, the two are presumed to be identical, and the burden of proof is effectively shifted to the patentee. Furthermore, parametric features that merely reflect known technical effects, without a substantive nexus to the technical problem being solved, are unlikely to sustain an inventive step argument.

The Semaglutide case (Supreme People’s Court, (2023) Zhi Xing Zhong No. 1282) delineated a critical boundary: sufficiency of disclosure and inventive step apply different standards when assessing post-filing supplemental experimental data. The former focuses on whether a person skilled in the art can carry out the invention, while the latter examines whether the technical effect is superior to that of the prior art. Applicants submitting supplemental data must rigorously distinguish between these two evidentiary purposes.

The lithium-ion battery safety case (CNIPA Decision No. 563221) demonstrated that where a claim defines parameters by mathematical formulas but the specification provides neither experimental data verifying those formulas nor an explanation of the implementation means, the sufficiency of disclosure requirement is not met.

Together, these two cases establish a core principle: the parametric target and the pathway to its realisation must both be disclosed. Where the specification has already established a preliminary link between the technical means and the intended effect, there remains room for supplemental data to be accepted at a later stage. Conversely, where only formulas are presented without any implementation pathway, the patent faces the risk of total invalidation.

Despite the aforementioned challenges, parameter-defined claims retain irreplaceable strategic value. By defining the scope of protection through parametric features, parameter-defined claims can encompass a variety of implementations that would be difficult to enumerate exhaustively by structural features alone, thereby effectively preventing competitors from circumventing patent protection through minor structural modifications. In cutting-edge fields such as battery materials and biopharmaceuticals, parameters are often a vital and feasible means of capturing the essence of an innovation. Chapter 8 of Part II of the Patent Examination Guidelines, together with relevant judicial interpretations, provides an institutional window for the submission of supplemental experimental data after the filing date.

The Supreme People’s Court and the CNIPA are systematically developing a normative framework for parameter-defined claims through landmark decisions, enabling applicants who master the rules to achieve more predictable outcomes in patent prosecution and validation.

Parameter-defined claims are a double-edged sword. Evaluating the distinguishing power of the chosen parameters, accurately grasping the differing evidentiary standards that sufficiency of disclosure and inventive step apply to experimental data, and ensuring that the specification discloses both the parametric targets and the pathways to their realisation are the keys to a successful patent strategy in this domain.