Studies were conducted to evaluate the effect of environmental conditions on physiological characteristics of seeds of sorghum genotypes viz., CO 24, CO 25, CO 26 and JH 35 during seed development and maturation. In the present study, a steady decline in moisture content of the seed was observed. Length and width of seed increased rapidly between seven to 35 days after 50 per cent flowering. A steep increase in the dry weight of seed was registered between 14 and 35 days after 50 per cent flowering, beyond that the increase was gradual. Water absorption per cent declined from 16.5 to 12.0 per cent between 7 to 28 days and increasing steadily beyond 42 days (22.1 per cent) after 50 per cent flowering. The germination potential of seeds improved with seed development and maturity. The root length, shoot length, dry weight of seedling, field emergence, seed recovery, seed yield and vigour index were highest in seeds harvested at 35 and 42 days after 50 per cent flowering. Seed vigour as estimated through stress tests viz., soaking seeds in ammonium chloride and D-manitol and accelerating ageing and exhaustion tests revealed the superiority of seeds having maximum germinability, vigour and viability at 35 and 42 days after 50 per cent flowering. These stages respectively correspond to physiological and harvestable maturity.