Seeds of three soybean cultivars (Santa Rosa, Viçoja e IAC-2) were divided in three sizes (large, medium and small), stored for one year in two differents environment, the first one with relative humidity of 35% and the other without control of humidity. During that year, at the Seed Laboratory of the Departamento de Agricultura e Horticultura-ESALQ-USP, those seeds were submited to germination and vigor (rapid aging) tests. The following conclusions could be drawn from the analysis and discussion of the results obtained: the germination was directly proportinal to seed size; there was a fall in germination from the first to the last time of testing, being the small seeds the most affected; the small seeds were the most vigourous; the ambient with 35% of relative humidity was the best on all the tests.