Aim To explore effects of telmisartan and angiotensin Ⅱ(AngⅡ)on expression of angiotensin converting enzyme-2(ACE-2)in thoracic aortic smooth muscle cells(A10 cells).Methods The expression of ACE-2 protein was tested by Western blotting analysis and the expression of ACE-2 mRNA was determined with reverse transcription-polymerase chain reaction(RT-PCR)technique.Results Telmisartan at the concentration from 10-8 to 10-5 mol/L dose-dependently enhanced the expression of ACE-2 protein;within 0 to 24 h,10-6 mol/L telmisartan increased ACE-2 protein expression in a time-dependent manner.Moreover,telmisartan at 10-6 mol/L upregulated the expression of ACE-2 mRNA.AngⅡ at 10-8 to 10-5 mol/L downregulated the expression of ACE-2 protein in a dose-dependent manner.Telmisartan at 10-6 mol/L obviously blocked the inhibition of 10-6 mol/L AngⅡ on the expression of ACE-2 protein and ACE-2 mRNA respectively.Conclusion Telmisartan not only up-regulates the expression of both ACE-2 protein and ACE-2 mRNA in A10 cells,but also antagonizes the inhibition of AngⅡon the expression of both ACE-2 protein and ACE-2 mRNA.