In this study, we demonstrated the antioxidant effect of the Caesalpinia sappan L. extract through the scavenging effect against 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and the protective effect on protein damage and PC12 cells against cupric ion/hydrogen peroxide. Its IC₅₀ value of the scavenging effect against DPPH radical was 7.7 ㎍. Protection of its extract against oxidative bovine serum albumin (BSA)damage induced by hydrogen peroxide was more effective than that of vitamin C. The protective effect on PC12 cells by hydrogen peroxide was shown to be more potent in is extract than in vitamin C. DNA fragmentation analysis also supports this result.