Aim To investigate the inhibition of naftopidil ramification YMⅢ on Wistar rat and spontaneously hypertensive rat(SHR) thoracic aorta smooth muscle cell(tASMC) proliferation induced by angiotensin Ⅱ(AngⅡ),and to explore the possible mechanisms. Methods Primary culture of tASMC from Wistar rat and SHR was established in vitro,and the effects of YMⅢ on tASMC proliferation induced by AngⅡ were determined by methyl thiazolyl tetrazolium(MTT) assay.The effects of YMⅢ on the expressions of angiotensinogen(AGT) and c-myc mRNA were detected by real-time reverse transcription polymerase chain reaction(RT-PCR). Results 0.1 μmol/L YMⅢ depressed Wistar rat and SHR tASMC proiferation and YMⅢ(0.01,0.05,0.1 μmol/L) depressed tASMC proiferation induced by AngⅡ in a concentration-dependent manner.YMⅢ(0.05～0.1 μmol/L) down-regulated the expression of AGT and c-myc mRNA on Wistar rat in 24 hours.YMⅢ(0.01,0.05,0.1 μmol/L) down-regulated the expression of AGT and c-myc mRNA on SHR in 24 hours. Conclusions Proliferation of tASMC induced by AngⅡ can be inhibited clearly by YMⅢ,the effect is more significant on SHR than on Wistar rat.The mechanisms may be related to down-regulating the expression of AGT and c-myc mRNA.