The ,Tananese oyster, Qstrer ,ggrcs is famous for its high production and fastgrowth and tb.e two native oysters, QsGrerx rirzatrrs and Ostrea pLicrtuIa, are welludapted to their Iacal environment. Cross breeding of gas with D. -iudrcris axedQ, pdicatu.b were attempted. paper deals with. tba probability of their interspecific hybridization, thesurvival and growth of the brid Iarvaa. The results of the experiment are asfollows 1 .The process of crass-breeding is easy to operate. The peroentage of fertilixartion in C. ggas×O. Pt2catuta is higher than in C, gigas×O. -iarctaras. 2. There is no any apparent difference in the time of development from eggs tothe straight-hinge larvae, but in the sedentary stages hybrids larvae grew faster thanthe native stocks. 3 .The size of hybrid straight-hinge Larvae are mainly influenced by maternalinheritance. . The range of variation in hybrid straight-hinge larvae is wider than that oftheir parents. 5. About 40,001) hybrid spats are reared in tanks and ready for further studies,