Nephrotoxicity is a common complication of cisplatin chemotherapy that limits its clinical use; however, the mechanisms underlying cisplatin-mediated nephrotoxicity are not fully understood. In this study, we investigated the role of anaphylatoxin C5a in the pathogenesis of cisplatin-mediated nephrotoxicity. Our data show that cisplatin-induced renal injury is significantly reduced in C5- or C5aR-deficient mice. However, pretreatment with C5 or C5a restores sensitivity to cisplatin-induced nephrotoxicity in C5-deficient mice. In wild-type mice, administration of cisplatin triggers the increased renal expression of multiple cytokines and caspases. This induction is diminished in C5-deficient mice, which is restored by pretreatment with C5 or C5a proteins. Interestingly, renal injury induced by cisplatin is similar between wild-type and CD59ab double knockout mice, and the formation of membrane attack complexes (MACs) by cisplatin in the kidney is diminished in C5-deficient mice, but not in C5aR-deficient mice. In conclusion, our findings suggest that C5a plays an important role in the pathogenesis of cisplatin nephrotoxicity. Likely, C5a binds to C5aR, leading to induction of proinflammatory cytokines and inflammation. The formation of MACs does not appear to contribute to the nephrotoxicity of cisplatin based on our study results.