Objective: To investigate the effects of let-7a on the migration and proliferation ability of vascular smooth muscle cells (VSMCs) cultured in vitro. Methods: VSMCs were isolated from the thoracoabdominal aorta of rats and then, were cultured and subcultured. Subsequently, the cultured VSMCs were assigned either to let-7a mimics (experimental group) or its negative control (negative control group) transfection using lentiviral expression vector, or no transfection treatment (blank control group). Transfection efficiency was estimated by expression of green fluorescence protein. In the cells of each group, the let-7a expression was detected by real-time PCR method, and the cell migration ability and proliferation status were determined by scratch test and CCK-8 assay, respectively. Results: Fluorescence microscopic observation revealed that the cell transfection efficiency reached more than 85%. Real-time PCR results showed that the let-7a expression was significantly higher in VSMCs of experimental group than that of either negative control group or blank control group (both P<0.01). The results of cell scratch test and proliferation measurement demonstated that both the migration and proliferative ability of the cells of experimental group were significantly decreased compared with those of negative control group and blank control group (all P<0.01), while all of the above parameters showed no obvious differences between negative control group and blank control group (all P>0.05) Conclusion: Let-7a has inhibitory effect on migration and proliferation of VSMCs cultured in vitro.