The effects of light quality on growth and maturation of gametophyte in Undaria pinnatifida were examined in an indoor culture at 20℃, 12 h light - 12 h dark cycle and 50 μmol m^{-2}s^{-1} using four different light emitting diodes (LEDs) and a fluorescent light. The relative growth rates of the male and female gametophytes under green LEDs showed high values, but that under red LEDs showed low values. The female gametophyte matured quickly under blue LEDs and a fluorescent light. On the other hand, they matured more slowly under white and green LEDs. Under red LEDs condition, the maturation of female gametophyte was not observed at all.