Objective To study the effects of simvastatin on proliferation and apoptosis in rat mesangial cells in vitro, and to investigate the signal pathways involved in apoptosis induced by simvastatin. Methods Cultured mesangial cells were treated with simvastatin. Proliferation of mesangial cells was examined by MTT assay. Simvastatin-treated apoptotic mesangial cells were observed by electron microscopy. Propidium iodide (PI) staining and flow cytometry were employed for quantitative measurement of apoptosis. Caspase-3 activation was determined by CaspGLOW Green Caspase-3 Staining Kit. Results (1)Simvastatin significantly inhibited proliferation of mesangial cells compared with control (P