The concentration of 50% scavenging ratio (SC50) and the scavenging rate constants (k) and stiochiometric factor (n) were determined when (-)-epigallocatechin gallate [(-)-EGCG] scavenging superoxide anion free radical (O2.-) and hydroxyl radical (.OH). The mechanism of scavenging active free radicals of (-)-EGCG and the promotion of (-)-EGCG free radical and its structure were analyzed in vitro. Our results suggest that the centers of scavenging reaction of (-)-EGCG are B, D, and A cycles, and each (-)-EGCG traps six O2.- or .OH. It is in accord with the value of stiochiometric factor n = 6.