Abstract: The genet ic distances made by RAPD technique on oysters demonstr ated tha t there are actual ly three natural spe cies , C .tal ienwhanensis , C .plicatula and C .rivularis , in nor ther n se a waters of China .They all belong to the same genus , Crassostrea .C . talienwhanensis, C .plicatula and C .gigas ar e sibl ing spe cies , but they are non-sibling species with C .rivularis .The result also proved that those individuals wi th typical ch aracters of morphology could be distinguished by the method of t radit ional classificat ion .