Rice plants cv. Koshihikari, were subjected to the biologically effective ultraviolet-B (UV-B_BE) radiation {daily dose : 0.0 (control) and 11.5 (enhanced UV-B) kJ m^-2} to investigate the effect of enhanced UV-B radiation on lipid peroxidation and to determine whether carotenoids and polyamines are involved in protection mechanism against enhanced UV-B radiation. Enhanced UV-B radiation significantly depressed plant dry weight. Malondialdehyde (MDA) content in rice leaves was increased by about 30% after 6 days of UV-B irradiation. Total carotenoid contents tended to slightly decrease with the UV-B irradiation, even though there was no significance. In rice leaves, 3 major polyamines, putrescine, spermidine and spermine are observed. All of the polyamine contents were increased with UV-B irradiation. The results suggest that enhanced UV-B radiation caused oxidative stress on lipids and that polyamines may serve as a biochemical protectant against increased UV-B radiation in rice plants.