Plants of soybean(cv.Enrei) were grown in pots(1/5000a) in a viny house. Temperature treatment was conducter for 10 days from the beginning of the flowering period(BFP) in the growth chambers under artificial light controlled at day/night air temperatures of 27/27, 32/27, and 37/27℃, respectively. the pollen viability at 37/27℃(89.4%) was significantly lower than 27/27℃(97.2%). In ouder to identify the sensitive stage to high temperature, the plants were treated for 2 days before BFP in the growth chambers controlled at 27/27 and 40/27 ℃, respectively, and the pollen viability of flowers opening after the treatment was investigates. By the treatment at 40/27℃, the pollen viability of flowers which opened at 4 days after the treatment(82.9%) was significantly lower than 27/27℃(97.3%). This indicates that floral buds at 4 to 5 days before flowering, which coincide with the microsporogenesis stage, are sensitive to high temperature. However, high temperature affected the pod setting ratio a little in both experiments. High temperature treatment was conducted by transferring the plants into the glasshouse under natural light before and after BFP. High temperature treatment at 7-1 days before BFP promoted vegetative growth and increased the pod setting ratio, while reducing the seed size. High temperature treatment at 14-8 days before BFP promoted floral differentiation on the second order racemes with compound leaves and increased the number of the floral buds, so that reduced the pod setting ratio. These results suggest that hight temperature at the microsporogenesis stage reduces pollen viabillity, however, pod setting ratio is affecter by the pollen viabillity.