Abstract: Due to the high diversity in fish species, their sex-determination mechanisms can be identified in almost all animals. Thanks to the advanced molecular biology techniques, there have been ground-breaking findings on the mechanisms of sex determination in fish, especially on the sex-differentiation genes in terms of the cloning, expression and the verification of their functions. In this article we reviewed the recent progress on the research of the sex-differentiation genes, the family of nuclear receptors, the steroidogenic enzyme-encoding genes, and the oocyte structure-related genes.