Abstract: In mammal,sex determination and differentiation are the consequence of sequential expression and interaction between many transcription factors and growth factors.The expression of SRY initiates the male pathway and induces the expression of many male specific genes,such as SOX9,AMH etc.The expression of FOXL2 in the undifferentiated ovary,and WNT-4 and DAX1 in female pathway made it no longer to be regarded as default pathway.Sex determination in birds is also controlled by genetic factors.EFT1 (female) and DMRT1 (male) were recommended recently as possible candidate genes for sex determination in birds.Many reptiles exhibit typical temperature sex determination.Temperature regulates the estrogen level and the sexual dimorphic expression of DMRT1 and SOX9 in the embryonic gonads during temperature sensitive period.Sex determination in the majority of amphibians is probably controlled by environmental factors,however,genetic factors such as DMRT1 and DAX1 may be involved in the differentiation of testis.Mechanisms of sex determination and differentiation vary considerably in fish.Many factors,especially sex steroidal hormones,were involved in the process.DMY,isolated by positional cloning in medaka,was regarded as the first sex-determining gene in non-mammals.All these seem to indicate that molecular mechanisms of vertebrate sex determination and differentiation are diversified.