We studied the effect over time of powdered green tea (PGT) on the triglyceride (TG) content and super-oxide dismutase (SOD) activity during adipose conversion of 3T3-L1 cells. In a 7-14-day culture with insulin, preadipocyte differentiation and TG accumulation were observed, but SOD activity was not significantly increased. After 21 days of culture, the TG concentration and SOD activity had further increased compared to their levels after 7 days of treatment ( p < 0.01). These results suggest that the intrinsic SOD activity had a preventive effect on the increase in TG concentration. When PGT and insulin were simultaneously added, the increase in TG content was markedly suppressed, and the SOD activity was significantly enhanced ( p < 0.01). These effects were most marked after 7 days of treatment, but became less thereafter because of the increase in intrinsic SOD activity. Thus, PGT had antilipogenic activity in the early phase and could be useful in preventing obesity.