Severe abdominal sepsis remains a significant cause of death in patients undergoing intra-abdominal infection, in despite of recent declines in overall mortality. There is a abundant evidence to suggest complement activation during sepsis. While there is great interest in complement by-products in human sepsis, few studies focus on the persistent consumption of complement components and its role in prognosis of sepsis. Complement C3 is indispensable community pathway for complement activation. In a way, the alteration of C3 levels can affect the whole status of complement biological functions.