Cai Pei (Chinese: 蔡培; pinyin: Cài Péi; Wade–Giles: Ts'ai P'ei; Hepburn: Sai Bai; 1884–1960) was a diplomat and politician in the pre-World War II Republic of China.

After his return to China, together with Liu Yazi he helped establish the literary and poetry society Nanshe.

In January 1928 Cai was appointed legislative secretary of the Ministry for Transportation under the Nationalist Government.

In March 1940, when the Reorganized National Government of China led by Wang Jingwei was established, Cai Pei was appointed Policy Affairs Vice-Minister for Commerce and Industry.

The following July he was charged with promoting "Sino-Japanese friendship" and sentenced to death by the Shanghai High Court.