Leydig cells play an important role in mammalian reproductive physiology and endocrine, the secretion of reproductive hormones are controlled by clock genes.Nr1d1(Rev-erbα), one of the clock genes, is a transcription factor that plays central roles in the regulation of circadian rhythms.It is still unkown that whether these clock genes exhibit a rhythmic expression and regulate testosterone production in mouse leydig cells.In this report, studies were carried out to investigate the rhythmic expression pattem of some clock genes at indicated time points and the relationship between Nr1d1 and testosterone.Mouse leydig tumor cells(MLTC1) and primary mouse ledyig cells(MLC) were synchronized with dexamethasone(DXM), and cells were collected every 4h interval from the beginning of 12h after the treatment.Real-time fluorescence quantitative PCR (RT-qPCR) was used to detect the rhythmic expression pattern of clock genes like Bmal1(Brain and muscle ARNT-like protein 1)、 Nr1d1 、 Per1(Period1) and Dbp(D site of albumin promoter binding protein).Rhythmic expression of testosterone secretion genes in MLC were also measured by RT-qPCR.The lentivirus vector pCD513B-U6 encoding Nr1 d 1 shRNA and nonsilencing negative control (shRNA-N) were constructed in our laboratory (Chen et al., 2016).