Symbiosis-specific changes in antioxidative ability and superoxide dismutase (SOD) isozyme in mycorrhizal asparagus plants through the inoculation with Fusarium oxysporum f. sp. asparagi (Foa, MAFF305556) were investigated. Dry weight of shoots and roots increased more in AMF (Gi, Glomus intraradices; GM, Gigaspora margarita)-inoculated plants than the control. Eight weeks after Foa inoculation, the incidence and severity of Fusarium root rot were alleviated in both AMF-inoculated plants, compared to the control, which were not alleviated. Superoxide dismutase (SOD) activity, ascorbate peroxidase (APX) activity, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity increased in both AMF-inoculated plants more than in the control before and after Foa inoculation, and increased in all asparagus roots due to Foa inoculation. As for SOD isozymes in roots before Foa inoculation, the Rf = 0.37 (Cu/Zn-SOD) band had a higher intensity in both Gi and GM compared to the control. Eight weeks after Foa inoculation, Rf = 0.33 and 0.37 (Cu/Zn-SODs) showed a higher intensity in both Gi and GM compared to the control. Though AM fungal difference appeared in the intensity of Rf = 0.25 (Mn/Fe-SOD); GM had a higher intensity than Gi, Cu/Zn bands had a clearly higher intensity than Mn/Fe band. These findings supposed that tolerance to Fusarium root rot in mycorrhizal asparagus plants might be closely associated with the changes in SOD activity and isozymes, especially in Cu/Zn-SODs.