We have studied the scavenging effects of different structures and configurations of schizandrins isolated from Fructus Schizandrae, a traditional Chinese herb, on active oxygen radicals with the method of spin-trapping technique. The active oxygen radicals were produced from human polymorphonuclear leukocytes (PMN) stimulated with phorbol myristate acetate (PMA). In addition, the scavenging effects of schizandrins on hydroxyl radicals (.OH) in Fenton's reaction and the scavenging effects on superoxide anions (O2-.) in both riboflavin/EDTA and xanthine/xanthine oxidase systems have also been studied. They are compared with the scavenging effects of both Vitamin C (Vc) and Vitamin E (VE). The experimental results have shown that the scavenging effect of schizandrin B (Sin B) on the active oxygen radicals is stronger than that of S(-) Sin B and R(+) Sin B. For schizandrins of the same molecular structures with different stereoconfigurations the scavenging effects of S type of the benzene ring on active oxygen radicals are stronger than those of R type and for schizandrins of the same stereoconfigurations with different structures the scavenging effects of schizandrin C (Sin C) on the active oxygen radicals are stronger than those of Sin B.