Abstract: The aim of present study were to characterize the pattern of seed development in precociously mature soybean seeds planted on different dates during its progression from germination to seedling growth and maturation and its effect on yield under temperate environment. Changes in seed quality (Viability and Germination) were monitored from developmental to maturation (growth stage R5 to R7) of soybean (Glycine max (L.) Merr.) in different planting dates. Information on the effect of planting date on seed fresh and dry weight, moisture content and germination of soybean is meager. A field experiment was conducted with four planting dates and two soybean cultivars to study the influence of planting dates on seed developmental traits for 2 years. Determinate cultivars (Epps, maturity group [MG] V) and indeterminate cultivar, Williams 82 [MG] 111) were planted on May 1st to August 1st at one month interval at the Agriculture Research Farm of the NWFP Agricultural University Peshawar, during 2000 and 2001. Seeds were harvested at 10-days interval from 35 to 75 days after anthesis (DAA) in all planting dates. Epps planted in early May gave maximum fresh, dry seed weight and moisture content. A steady decrease in fresh and dry weight and moisture content were observed with delay in sowing of soybean. An inverse relationship was noted in Williams 82 regarding fresh, dry weight and moisture content in all planting dates. Water per seed increased up to 100% DAA, after which no further increase occurred. Moisture content declined for the whole seed, respectively, from above 75 and 65% at 95 DAA to 65 and 50% at 140 DAA in both cultivars. Decrease in seed moisture content during development was accompanied by increase in desiccation tolerance and germination, reaching maximum at physiological maturity in both cultivars. Fresh and dry seed germination increased linearly in both varieties. Mean rate of change in germination was more pronounce in Epps as compared to Williams 82. Immature seeds in both cultivars during early developmental stage did not germinate in all planting dates.