The effects of the irradiation of weak white light on the growth of the red yeast Rhodotorula glutinis and its production of carotenoids were investigated. The ability of beta-carotene and torularhodin, which are final products of carotenoid biosynthesis in R. glutinis, to quench singlet oxygen has also been investigated. Weak white light irradiation that has no effect on the growth of Saccharomyces cerevisiae inhibited the growth of R. glutinis. Simultaneously, the production of torularhodin by R. glutinis markedly increased. In a mutant of R. glutinis, which exhibited increased production of torularhodin, an increase in torularhodin production was shown as a result of light irradiation during the logarithmic growth phase. An experiment using 3-(1,4-epidioxyl-4-methyl-1,4-dehydro-1-naphtyl) propionic acid clarified that torularhodin inhibited 2,5-diphenyl-3,4-benzofran decomposition by singlet oxygen quenching more strongly than did beta-carotene. This result is consistent with the report that carotenoids having a longer polyene chain may exhibit a more potent ability to quench singlet oxygen. These results suggest that the biosynthesis of carotenoids in R. glutinis may play an important role in protecting against oxidative damage caused by light irradiation, and in particular, torularhodin which has a potent singlet oxygen quenching ability may be important. We suggest that acquisition of the ability to produce torularhodin may be an important property for this yeast to promote its wider distribution in the natural world.