Objective To evaluate the effect of autophagy inhibitor 3-methyladenine (3-MA) on phenotype transformation and proliferation of rat pulmonary arterial smooth muscle cells (PASMCs).Methods Cultured PASMCs were treated with different concentrations of 3-MA (low-dose group,2.0 mmol/L;middle-dose group,4.0 mmol/L;high-dose group,8.0 mmol/L;control group,0 mmol/L).The protein expression of LC3 Ⅱ,OPN and Vimentin was detected by Western blotting.Cell proliferation was detected by MTT assay.Results The autophagy of PASMCs was decreased with the increase of the concentration of 3-MA.Compared with the control group,significantly down-regulated protein expression of LC3 Ⅱ,OPN and Vimentin was observed in 3-MA-treated cells,with significantly lower proliferation activity.Conclusion The autophagy inhibitor 3-MA significantly down-regulated the expression of LC3 Ⅱ,OPN and Vimentin in PASMCs,with inhibiting the proliferation of PASMCs.