Objective：To detect the expression of specificity protein 1（SP1）in the renal tissues of rats with Thy-1 nephritis（Thy-1N）and in the glomerular mesangial cells（GMCs）stimulated with sublytic C5b-9，and investigate the role of SP1 expression in sublytic C5b-9-induced GMC proliferation. Methods：Rat Thy-1N was induced，and the cultured rat GMCs were stimulated with sublytic C5b-9. The expression of SP1 in the renal tissues of rats with Thy-1N（in vivo）and in the GMCs stimulated with sublytic C5b-9（in vivo）was detected by real-time PCR and Western blot，respectively. Meantime，SP1 expression plasmid（pEGFP-N1/SP1-His）and SP1 shRNA（shSP1）were constructed. Above-mentioned plasmids and control plasmids were transfected into rat GMCs followed by sublytic C5b-9 stimulation or not. The expression levels of SP1 were evaluated by real-time PCR and Western blot，and the cellular proliferation was determined by CCK-8. Results：The expression levels of SP1 in the renal tissues of rats with Thy-1N and in the GMCs stimulated with sublytic C5b-9 were markedly increased with similar time points. SP1 overexpression could markedly promote GMCs proliferation，while SP1 knockdown could obviously reduce sublytic C5b-9-induced GMCs proliferation. Conclusion：Sublytic C5b-9 promotes rat GMCs proliferation through up-regulation of SP1.