Hyperuricemia is associated with kidney complications including glomerulosclerosis and mesangial cell (MC) proliferation by poorly understood mechanisms. The present study investigated the underlying mechanisms that mediate uric acid (UA)-induced MC proliferation. A rat MC line, HBZY-1, was treated with various concentrations of UA in the presence or absence of a specific extracellular regulated protein kinases1/2 (ERK1/2) inhibitor (U0126), apocynin. UA dose-dependently stimulated MC proliferation as shown by increased DNA synthesis and number of cells in the S and G2 phases in parallel with the up-regulation of cyclin A2 and cyclin D1. In addition, UA time-dependently promoted MC proliferation and significantly increased phosphorylation of ERK1/2, but not c-Jun N-terminal kinase and p38 MAPK in MCs as assessed by immunoblotting. Inhibition of ERK1/2 signaling via U0126 markedly blocked UA-induced MC proliferation. More importantly, UA induced intracellular reactive oxygen species (ROS) production of MCs dose dependently, which was completely blocked by apocynin, a specific NADPH oxidase inhibitor. Toll-like receptor (TLR)2 and TLR4 signaling had no effect on NADPH-derived ROS and UA-induced MC proliferation. Interestingly, pretreatment with apocynin inhibited ERK1/2 activation, the up-regulation of cyclin A2 and cyclin D1 and MC proliferation. In conclusion, UA-induced MC proliferation was mediated by NADPH/ROS/ERK1/2 signaling pathway. This novel finding not only reveals the mechanism of UA-induced MC cell proliferation, but also provides some potential targets for future treatment of UA-related glomerular injury.