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Zu Gengzhi (simplified Chinese: 祖暅之; traditional Chinese: 祖暅之; pinyin: Zǔ Gèngzhī; Wade-Giles: Tsu Kengchi; 480 - 525[1]), courtesy name Jing Shuo (景烁), sometimes referred to as Zu Geng; was a Chinese mathematician. He was the son of another famous Chinese mathematician, Zu Chongzhi.

Zu Gengzhi discovered the "Zu Geng's Principle" (continuing work by Liu Hui), stating that "The volumes of two solids of the same height are equal if the areas of the plane sections at equal heights are the same." This is same as Cavalieri's principle, but was discovered about 1100 years earlier.

He is credited with the invention of the astronomical sighting tube, which Shen Kuo and Wei Pu would later improve during the 11th century.