With the purpose of determining the best harvesting time for obtaining good quality seeds of cotton (Gossypium hirsutum L.), one experiment was conducted with three cultivars and eleven promising strains in Capinópolis-MG, during the 1981/82, 1982/83 and 1983/84 growing seasons. The samples were taken at three different times: A - at 40% of open bolls; B - at 70% of open bolls; and C - at open top bolls. The seed samples were sent to the seed laboratory at EPAMIG/Uberaba for determination of germination rate, vigor (first count) and 100 seed weight. In 1981/82, the germination and 100 seed weight slightly decreased with prolonged time in the field without affecting the real seed quality. In 1982/83 and 1983/84, significant effects among cultivars and strains were observed for the 100 seed weight and among harvesting times for all three parameters. The harvesting time C (open top bolls) in 1983/84 produced low quality seeds. The highest seed quality was obtained when the harvest was done at either the 40% or 70% of open bolls stages.