Clover plants (Trifolium repens L.) were inoculated with arbuscular mycorrhizal (AM) fungus, Glomus intraradices, in pot and split-root experiments. The mycorrhizal colonization and antioxidase activities in roots were measured for the influence of Glomus intraradices on the root antioxidase activities and the systematization of the influence. Results indicated that G. intraradices significantly enhanced the activities of SOD, POD, CAT in roots in the pot experiment, suggesting an increased antioxidase activity by AM fungus. For the plants with half roots inoculated with G. intraradices in the split-root experiment, the activities of SOD, POD also increased in the other half roots without G. intraradices, suggesting the systematization of the increase in antioxidase by AM fungus. Given that the antioxidase system is the physilogical and biochemical basis of the resistance to diverse stresses in plants, this systematical increase may contribute to the protection of the entire roots, not of the infected ones only.