In this study, the effects of dexamethasone(Dex) on the DNA ynthesis and proliferation of vascular smooth muscle cells(VSMC)were studied by 3H-thymidine(3H-TdR) incorporation and counting cell number. With Northern blot analysis and measuring the amount of nitrite, we observed the expression of inducible nitric oxide synthase (iNOS)gene in VSMC of control and treated by tumor necrosis factorα(TNF-α),TNF-α+Dex respectively.It was found that the DNA synthesis and proliferation of VSMCwere obviously inhibited by dexamethasone,the inhibitory rate was proportional to the dose and the duration of dexamethasone treatment.The results ofNorthern biotting and quantity of nitrite in culturemedium showed that dexamethasone obviously inhibited the expression of iNOS gene and nitric oxide (NO)production in VSMC induced with TNF-α. These results indicate it is not by increasing the NO production that dexamethasone inhibits the DNA synthesis and proliferation of VSMC.