Objective To study the impacts of losartan and angiotensin Ⅱ (AngⅡ) towards the matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1) secreted by rat vascular smooth muscle cells (VSMCs).Methods The rat VSMCs were isolated and cultured with different concentrations of AngⅡ and losartan for 24 hr, then the Western blot and RT-PCR methods were performed to observe the impacts of the above combined incubation towards the production of MMP-9 and TIMP-1 genes and proteins by VSMCs.Results AngⅡ could promote the VSMC to produce MMP-9 protein and gene with a concentration-dependent manner, while it had no effect towards TIMP-1, so the MMP-9/ TIMP-1 ratio would increase; losartan would inhibit the MMP-9 protein and gene production with a concentration-dependent manner, while promote TIMP-1 to increase, so that the ratio of MMP-9/TIMP1would decrease; the combined action of losartan and AngⅡ would result in the same results in the changes of MMP-9 and T-IMP-1 genes and proteins as losartan did alone.Conclusions The comparison of AngⅡ, losartan and the combination towards the MMP-9 and TIMP-1 production changes by VSMC indicated that losartan would inhibit the effects of AngⅡ, therefore reducing the MMP-9/TIMP-1 ratio, which might be the anti-atherosclerotic mechanism of losartan.