Zu Chongzhi (祖冲之, pinyin Zǔ Chōngzhī, Wade-Giles Tsu Ch'ung-chih) (429-500) was a Chinese mathematician and astronomer during the Song and Qi Dynasties (of the Southern Dynasties).

His ancestors hailed from Qiu district, Fanyang commandry (today in Laiyuan county, Hebei province). To flee from the ravages of war, Zu Chongzhi's grandfather Zu Chang moved from Hebei, in north China, to south of the Yangtze River, as part of the massive population movement during the Eastern Jin Dynasty. Zu Chang at one point held the position of "Minister of Great Works" (Dàjiàngqīn) within the Song Dynasty (420-479) and was in charge of government construction projects. Zu Chongzhi's father also served the court and was greatly respected for his erudition.

Zu Chongzhi was born in 429 in Jiankang (today Nanjing). His family had historically been involved in astronomy research, and from when he was a child Zu Chongzhi was exposed both to astronomy and to mathematics. When he was only a youth his talent earned him much repute. When Emperor Xiaowu heard of him, he was sent to an Academy, the "Huálín Xuéshěng", to perform research. In 461 in Nanxu (today Zhenjiang in Jiangsu) he was engaged in work at the office of the local governor.

His achievements included the Daming calendar introduced in 465 and deriving two approximations of pi, 355/113 (密率, Milu) and 22/7 (约率, Yuelu).

Asteroid 1888 is named after him.