Abstract: AIM To investigate the anti-proliferation and cell cycle arrest effects of curcumin on rat vascular smooth muscle cells (VSMCs) and to observe the expression changes of cyclinD1 and p21waf1/cip1. METHODS VSMCs were primarily cultured by explant method from the thoracic aorta of SD rats. The VSMCs were treated by curcumin with different concentrations. The viability and proliferation of VSMCs were assayed by MTT and the changes of cell cycle of VSMC induced by curcumin were observed by flow cytometry. Western blotting was applied to detect the expression of cyclinD1 and p21waf1/cip1. RESUITS Administration of 7.5-120 μmol/L curcumin for 24-72 hours significantly inhibited VSMCs proliferation in a dose-and time-dependent manner (P<0.05). 30 μmol/L curcumin significantly blocked the cell cycle progression in proliferative VSMCs, decreased cells in S, G2/M phase (P<0.05) and increased cells in G0/G1 phase (P<0.05). 30 μmol/L curcumin significantly down-regulated cyclinD1 expression and up-regulated p21waf1/cip1 expression. CONCLUSION Curcumin inhibits cell proliferation and arrests the cell cycle progression. These effects may partly be related to the expression changes of cyclinD1 and p21waf1/cip1.