Aim To investigate the effects of Doxazosin on the proliferation of rat vascular smooth muscle cells (VSMCs) cultivated in vitro. Methods Various concentrations of Doxazosin were added to the cultured rat VSMCs. 3 H TdR incorporation were used to detect proliferation of VSMCs. Results Doxazosin inhibited the proliferation of VSMCs. The proliferation of NIH3T3 cells,which do not express α 1 receptors, also were inhibited. Pretreatment of cells with phenoxybenzamine, an irreversible α 1 receptor antagonist, did not chang the effect of Doxazosin. Conclusions These results suggest that doxazosin inhibited the proliferation of VSMCs through a mechanism unrelated to α 1 receptor.