The expression of carotenoid biosynthetic genes in sweet pepper (Capsicum annuum L.) fruit during ripening and effects of light irradiation on fruit ripening were investigated. Fruits were harvested at the beginning of ripening, followed by light irradiation at a photosynthetic photon flux density of 100 μmol・m⁻²・s⁻¹. Gene expressions of phytoene synthase (Psy), β-carotene hydroxylase (CrtZ-2), and capsanthin/capsorubin synthase (Ccs) were markedly induced after 1 day of light irradiation. Each expression was 207, 8, and 6-times higher than the dark control, respectively. Other carotenoid biosynthetic genes: phytoene desaturase (Pds), ζ-carotene desaturase (Zds), lycopene β-cyclase (LcyB), zeaxanthin epoxidase (Ze), and violaxanthin de-epoxidase (Vde), were also induced to 2–3-fold higher than the dark control. Light-irradiated fruits reached full redness in five days. These results suggest that light irradiation of harvested fruits induces a marked increase in the expression of Psy and other carotenoid biosynthetic genes such as CrtZ-2 and Ccs, followed by the accumulation of capsanthin in the sweet pepper fruit.