Two assays were conducted to evaluate the utilization of solutions with different osmotic potentials, on substrates at the laboratory, to simulate the conditions of a water stress, as a test of vigor. In the first assay, the treatments consisted of a combination of six osmotic potentials (0, -3, -6, -9, -12 and -15atm), utilizing mannitol as the solute and seeds from five soybean genotypes: IAC 11, IAC 8, UFV 15, FT 11 and Garimpo, harvested when physiological maturity was reached. In the second, seeds 30 day overdue harvest maturity were used, and the experimental conditions were similar to those in the first assay. The assays were a randomized complete block with four replications, and the treatments were arranged in a factorial design (5 x 6), in a combination of five soybean genotypes and six osmotic potentials. In the evaluation of osmotic stress, it was recorded: normal seedlings and dry matter weight per seedling. It was concluded that: 1) the utilization of osmotic stress in the evaluation of vigor of soybean seeds was not promising, because it was verified that, there was differentiation among genotypes concerning to physiological quality of the seeds when the harvest was delayed; 2) the fact of some genotypes present higher germination of the seeds with the enlargement of osmotic potential when the harvest was delayed, restricts the utilization of the osmotic stress as a test of vigor to soybean seeds.