As lower vertebrates, f ishes have complex modes of sex determination. From the cytogenet ic perspective, only a small proportion of f ish species have heteromorphic sex chromosomes. At the present stage sex determination can only be explained via .. genetics.. rather than .. genes.. in most species. Nevertheless, genes associated with sex determination and male development were identified in a model fish medaka, Oryzias latipes. Sequences or genetic markers specif ic to certain sex chromosomes were reported in some f ishes. These f indings lay the groundwork for further studies on the function and regulat ion of sex genes aiming at elucidation of the mechanism of sex determination, and provide potential tool for sexing f ish. In this mini..review , progress in the past few decades in both cytogenetic and molecular genetic studies on sex determination of f ish were summarized. Prospects, signif icance and possible future directions of the studies on fish sex determination were also discussed.