Abstract : By analysing an excerpt of Jia Gongyan’s commentary on the Rites of Zhou, this paper uncovers different mathematical knowledge as compared with that previous known from Chinese mathematical sources, for example the Nine Chapters on Mathematical Procedures. The differences cover several aspects: structure of procedure, cognition of numbers and figures, mode of reasoning, and the use of counting rods. On the other hand, similar mathematical knowledge to that of Jia Gongyan exists in other Confucian canons. Moreover, a scholar, Wang Zhenru, commented on Confucian canons with Jia Gongyan, and later commented on mathematical books with Li Chunfeng. This paper emphasizes the necessity for further study of the mathematical knowledge in Confucian canons, and the relationship between Confucianism and mathematics.