The dry weight accumulation rate in soybean (Glycine max (L.) Merrill) seed was measured for 2 yr (1971–72), utilizing four cultivars and several planting dates within each year. Rates observed ranged from 3.38 to 8.32 mg/seed/day. There were significant differences among cultivars and planting dates. There was no significant relationship between the rate of accumulation and grain yield, seed weight or final seed number. Grain yield was closely correlated with final seed number both within each year and across both years.