Article 31 of the Patent Law of the People's Republic of China stipulates:

A patent application for an invention or utility model shall be limited to one invention or utility model. Two or more inventions or utility models that belong to a single general inventive concept may be filed as one application. 

A design patent application shall be limited to one design. Two or more similar designs for the same product, or two or more designs for products that fall into the same category and are sold or used as a set, may be filed as one application.

Rule 40 of the Implementing Regulations of the Patent Law of the People's Republic of China stipulates:

1.    In accordance with the provisions of the second paragraph of Article 31 of the Patent Law, if multiple similar designs of the same product are filed as one application, the other designs of the product shall be similar to the basic design specified in the brief description. The number of similar designs in one design patent application shall not exceed 10.

2.    The term "two or more designs for products that fall into the same category and are sold or used as a set" as mentioned in the second paragraph of Article 31 of the Patent Law refers to products that belong to the same main category in the classification table, are customarily sold or used together, and whose designs share the same design concept.

Based on the above laws and regulations, the author highlights the key points for the examination of unity in design patent applications as follows:

1.    In principle, a design patent application shall be limited to one design. 

According to the updated 2023 " Guidelines for Patent Examination," the design of an "assembled product" also constitutes one design. For example, a juicer/ice shaving machine comprising a juicing cup, ice shaving cup, and a base.
It should be noted that if two or more partial designs of the same product that are not connected are functionally or design-related and form a specific visual effect, they can also be deemed as one design. For example, the design of the two arms of a pair of glasses. 

2.    Two or more similar designs of the same product

According to Article 31.2 of the Patent Law, two or more similar designs of the same product can be filed as one application.
The number of similar designs in one design patent application shall not exceed 10. If it exceeds 10, the examiner shall issue an office action, and if the applicant does not amend the application documents to overcome the defect, the patent application shall be rejected.

(1) Same product

According to the second paragraph of Article 31 of the Patent Law, each design in an application shall be a design of the whole or part of the same product.

Take the design of a dining plate as an example. If the designs are respectively for a dining plate, dish, cup, and bowl, although these products belong to the same main category in the International Classification for Industrial Designs, they do not belong to the same product.

(2) Similar designs

According to the first paragraph of Rule 40 of the Implementing Regulations of the Patent Law, other designs of the same product shall be similar to the basic design specified in the brief description. When determining similar designs, each other design shall be compared with the basic design separately.

During the preliminary examination, applications involving similar designs should be examined to see if they obviously do not comply with Article 31.2 of the Patent Law. Generally, upon overall observation, if the other designs and the basic design have the same or similar design features, and the differences lie in minor local changes, conventional designs of such products, repeated arrangement of design units, conventional changes in the position and/or proportion of the partial design within the whole product, or changes only in color elements, it is usually considered that they belong to similar designs.

3.    Design of a Set of Products

According to the second paragraph of Rule 40 of the Implementing Regulations of the Patent Law, two or more designs for products that fall into the same category, are sold or used as a set, and share the same design concept can be filed as one application.

(1) Same category

According to the second paragraph of Article 31 of the Patent Law and the second paragraph of Rule 40 of the Implementing Regulations of the Patent Law, one of the conditions for filing two or more designs as one application is that the products of these designs belong to the same category, that is, they belong to the same main category in the International Classification for Industrial Designs.

It should be noted that belonging to the same main category is not a sufficient condition for a multiple application; it must also meet the requirements of being sold or used as a set and sharing the same design concept as stipulated in the second paragraph of Article 31 of the Patent Law and the second paragraph of Rule 40 of the Implementing Regulations of the Patent Law.

(2) Sold or used as a set

(i) Sold as a set

Sold as a set means that the products are customarily sold together, such as a multi-piece set of bedding composed of a bedspread, bed sheet, and pillowcase. Products arbitrarily bundled for promotional purposes, such as a schoolbag and a pencil case, are not considered customarily sold together even if the pencil case is given away with the purchase of the schoolbag, and thus they cannot be filed as a set of products.

(ii) Used as a set

Used as a set means that the products are customarily used together, meaning that using one product leads to the association of using another product or several other products, rather than using all the products simultaneously at the same time. For example, coffee utensils such as a coffee cup, coffee pot, sugar bowl, and milk jug.

(3) Same design concept

The same design concept means that the design style of the products is unified, that is, the design made to the shape, pattern, or combination thereof, as well as the color and the combination of shape and pattern, is consistent.

(4) A set of products should not include similar designs

A design patent application for a set of products should not include similar designs of any one or several products. For example, a design patent application for a set of products that includes a dining bowl and a plate should not also include two or more similar designs of the said bowl or plate.

For applications that do not comply with the above provisions, the examiner shall issue an office action requiring the applicant to amend the application documents.

4.    Each Design in a Multiple Application Must Meet the Allowance Criteria individually

It should be noted that whether the multiple application involves two or more similar designs of the same product or a set of products, each design or the design of each product must not only comply with the relevant provisions for multiple applications mentioned above but also meet other criteria individually. If one of the designs or the design of one product does not meet the allowance criteria, that design or the design of that product must be deleted; otherwise, the patent application cannot be granted.