The San Diu (also known as San Deo, Trai, Trai Dat and Man Quan Coc) are an ethnic group in Vietnam.

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

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