The San Diu (also known as San Deo, Trai, Trai Dat and Man Quan Coc) are an ethnic group in NorthVietnam. They are believed to have migrated from the Guangdong province in 1600.

The group's estimated population as of 2000 is 117,500. They speak an archaic variant of Cantonese. The major religion is Taoism, with elements of animism and ancestor-worship. About 400 are Catholic Christians; a few are evangelical protestants. The major concentration is in Quang Ninh province.