Two antioxidant compounds were isolated from C. sappan L by multiple steps of column chromatography and thin layer chromatography in succession with superoxide scavenging assay as activity monitor. Structures of the two compounds were determined by spectroscopic methods as 1',4'-dihydro-spiro[benzofuran-3(2H),3'-[3H-2]benzopyran]-1',6',6',7'-tetrol (compound 1) and 3-[[4,5-dihydroxy-2(hydroxymethyl) phenyl]-methyl]-2,3-dihydro-3,6-benzofurandiol (compound 2). Characterization of antioxidant properties of these two compounds was done by determining the inhibitory effect on xanthine oxidase activity as well as scavenging effect on superoxide anion and hydroxyl radicals. Our results indicated that compounds 1 and 2 inhibited xanthine oxidase activity and scavenged superoxide anion and hydroxyl radicals. Compounds 1 and 2 possessed similar radical scavenging activities as ascorbic acid, and they were more effective than other well-known antioxidants such as alpha-tocopherol, beta-carotene, and BHT. As inhibitors of free radical formation, compounds 1 and 2 were more effective than all the other antioxidants tested. In conclusion, compounds 1 and 2 can be regarded as primary antioxidants with radical-scavenging and chain-breaking activities as well as secondary antioxidants with inhibitory effect on radical generation.