We investigated the effect of culture temperature on the maximum specific growth rate and cellular sugar accumulation, and the effect of a temperature shift on the sugar accumulation of cells of an Antarctic green alga, Chlorella vulgaris SO-26, in a batch culture system. Decreases in temperature appeared to correlate with decreases in the maximum specific growth rate; on the other hand, the cellular sugar content showed a reverse tendency against temperature. We attempted to use this tendency to improve sugar productivity in Chlorella. First, we cultured Chlorella at 20 degrees C during the logarithmic growth phase to obtain a high specific growth rate. The culture temperature was then shifted from 20 degrees C to 14 degrees C during the stationary growth phase to increase the cellular sugar content. As a result, we obtained a 25% increase in sugar production over that obtained by culture at 20 degrees C throughout the culture.