Cheng Yi (, 1033–1107), courtesy name Zhengshu (正叔), also known as Mr. Yinchuan (伊川先生), was a Chinese philosopher born in Luoyang during the Song Dynasty. He worked with his older brother Cheng Hao (程灏). Like his brother, he was a student of Zhou Dunyi, a friend of Shao Yong, and a nephew of Zhang Zai. The five of them along with Sima Guang are called the Six Great Masters of the 11th century by Zhu Xi.

Cheng entered the national university in 1056, and received the "presented scholar" degree in 1059. He lived and taught in Luoyang, and declined numerous appointments to high offices. In 1086, he was appointed expositor-in-waiting and gave many lectures to the emperor on Confucianism. He was more aggressive and obstinate than his brother, and made several enemies, including Su Shi, the leader of the Sichuan group. In 1097, his enemies were able to ban his teachings, confiscate his properties, and banish him. He was pardoned three years later, but was blacklisted and again his work was banned in 1103. He was finally pardoned in 1106, one year before his death.