To investigate the mechanism of control of Chara oospore germination by light, tests were made on the effects of white and coloured lights on the germination of oospores of Chara delicatula. The oospores germinated well under white light, but scarcely at all in the dark. Red light was effective in causing germination, but blue and far-red lights had little effect. Germination was induced effectively by brief irradiation with red light. Moreover, the effectiveness of red light on induction of germination was diminished considerably by subsequent irradiation with blue or far-red light, whereas the inhibitory effect of blue and farred lights on induction of germination was eliminated by subsequent irradiation with red light. These facts suggest that a phytochrome system may participate in the germination of Chara oospores.