This study was conducted to determine the effect of planting date on soybean seed quality. The cultivars evaluated were Cristalina, IAC-2, Tropical, Doko, and IAC-8. The sowing dates were stablished between October 29, 1983 and January 7, 1984 (10/29, 11/11, 11/25, 12/10, 12/24 and 01/7), at Lucas do Rio Verde in Mato Grosso State, Brazil. In the plantings carried out at late maturing October and early November, the cultivar Tropical, which is a late cultivar, showed the best physiological seed quality. The other cultivars showed problems with vigor and percent germination due to high moisture during the maturation period. There is a probability to occur excessive rains falls and high temperatures even during the maturation period of the cultivars sown in the proper planting date (December 10), as it occurred with the cultivars Cristalina and IAC-2. ln this experiment it was also found that the stink bugs control has to be constantly done from the begining of the pod formation until the complete seed maturation.