Aim: To evaluate the protective role of membrane cofactor protein (MCP, CD46)on complement-dependent injury. Methods: MCP was separated by ion exchange chromatography on a DEAE sephadex A-50 column from pig erythrocyte ghosts.Its protective effect was tested in models such as cobra venom factor (CVF)induced platelet metamorphosis and aggregation, human serum-induced injury in isolated working guinea pig heart and reverse passive Arthus reaction. Results:MCP inhibited CVF-induced platelet metamorphosis with an IC50 of 56.7 mg/L+2.6mg/L, and prevented injury induced by activated complement in isolated working guinea pig hearts. In the rat model of reverse Arthus reaction, MCP relieved the skin lesions induced by immune complexes. Conclusion: MCP has a protective effect against complement-dependent injury.