Objective To study the regulation role on molecular level of hCG on P450scc,P450c17 and 3?HSD in adult mouse Leydig cells. Methods Leydig cells of adult mice were cultured in vitro for 1 and 8 hours with or without hCG,then P450scc,P450c17 and I,VI total 3?HSD mRNA levels were measured respectively by the semi quantitative RT PCR as well as Scal restriction endonuclease incised methods.Meanwhile,the testosterone contents were measured in two groups. Results 1.In stimulated group Leydig cells cultured for 1 and 8 hours with hCG,the testosterone contents were higher significantly than those in control groups(1 hour P 0.05),but the ratio of type VI/I 3?HSD mRNA gradually increased. Conclusion hCG can stimulate the transcription of P450scc,P450c17 and type VI 3?HSD in adult mouse Leydig cells.