With the objective od determining the effect od planting date on soybean seed quality, "Paraná", "Bragg", "Santa Rosa" and "Viçoja" cultivars, from the "Ensaio Nacional de Ecologia de Soja" (National Trial for Soybean Ecology), were studied. several arrangements cultivars x date of planting were evaluated in terms of seed germination. The analysis of variance for seed germination indicated significante differences for planting dates and cultivars. Seed of eraly season cultivars from the Oct. 20 planting showed the lowest germination percentage. Seed from de Dec. 20 planting were poor in qulity for all cultivars. Best seed quality was obtained from planting carried out on November and beginning of December. The maisn cause of low seed quality for the early season cultivars harvested on February and beginning of March is the association of temperature, higher than in April, with rainfall. Neverthless, seed from the Dec. 20 planting was damaged by the attack of high population of stink bugs. This is specially true for the late season cultivars.