The protective role of uric acid against photooxidative stress was examined using the silkworm, Bombyx mori. The production of uric acid in the larvae was artificially reduced by feeding allopurinol, an inhibitor of uric acid synthesis. In the uric acid-deficient group, the average survival period under UV irradiation was shortened to 74% that of the non-treated group. The uric acid-deficient group was also hypersusceptible to the phototoxicity induced by rose bengal, and the average survival period was reduced to 52% that of the control group. These results proved that uric acid is effective in conferring protection against photooxidative stress in the silkworm.