The coloration of sea ice by the ice algae occurred in austral autumn and spring at Syowa Station, Antarctica and in winter at Toetoko in Lake Saroma, Japan. The ice algal proliferation at both localities seemed to proceed through a similar process and under common environmental conditions. The solar radiation and the stability of the undersurface of sea ice as principal factors were compared between the two localities, particularly during the proliferation period of ice algae. Ordinarily it seemed that the ice algae proliferated between the beginning of March and the end of March at Syowa and from the end of January to the end of February at Toetoko. The amount of solar radiation supplied during the algal proliferation period ranged from 1500 to 2500 cal/(cm)^2/10 days. No significant difference in the amount of solar radiation was recognized between Syowa and Toetoko. The mean air temperature ranged from -6°to -9℃ at Syowa Station. The sea ice did not grow or melt and its undersurface was stable during the algal proliferation period. At Toetoko, the temperature was between -7°and -8℃ and the stability of the undersurface of sea ice was observed. The amount of solar radiation penetrating through the sea ice was examined at Toetoko. The percentage of penetrated solar radiation to the incident solar radiation varied from 4 to 36% depending upon the surface condition of the sea ice.