Objective：To investigate the regulatory effect of dexamethasone on NF-κB and its target gene cyclinD1 in human prostate cancer cell line PC-3, so as to explore the anti-proliferation mechanism of dexamethasone. Methods.. The inhibitory effects of dexamethasone on growth of PC-3 cells were determined by MTT. The basic transcriptional activity of NF-κB in many kinds of tumor cells and the effects of dexamethasone on the activation of PC-3 cell NF-κB were determined by reporter gene assay. The expression of cyclinD1 protein was determined by Western blots. Results： Dexamethasone inhibited the growth of PC- 3 cells and NF-κB was constitutively activated in the PC-3 cells. Dexamethasone also inhibited the activation of NF-κB and down-regulated the expression of cyclinD1 protein in PC-3 cells. Conclusion： Dexamethasone can inhibit cell growth of prostate cancer cell line PC-3 ,which might be related to the inhibitory effect of dexamethasone on the transcriptional activation of NF-κB and cyclinD1 protein.