In order to determine the appropriate sowing dates, seed rates and their interaction effects on yield and yield components, oil and protein contents of soybean variety Sari, a split-plot experiment based on a randomized complete blocks design with four replications was carried out at Qaemshahr Gharakeil Agriculture Research Station in 2009. Five sowing dates including 15^th May, 31^th May, 15^th June, 1^th July and 16^th July were considered as main plots and three different seed rates including 60, 75 and 90 kg ha^-1 as the sub-plots. The results showed that all of yield components were affected by sowing dates and also seed rates had a significant effect on the number of pods per plant. Although due to increasing seed rates, yield components, such as pods per plant were decreased, but because of the increasing number of plants per square meters, seed yield not decreased significantly. Therefore for economically saving 60 kg ha^-1 of seed rates will be preferred. In this study high mean value of seed yield, biological yield and 1000-seed weight was achieved in first sowing date and all of the yield component characters were decreased in late sowing dates. Harvest index was increased in late sowing dates and it was not significantly affected by seed rates. Sowing dates and seed rates had not significant effects on oil and protein percentages, but due to significant effects of sowing dates on seed yield, oil and protein yields were significantly affected by sowing dates. In this study higher seed yield was belonged 60 kg ha^-1 of seed rate in first and second sowing dates which have not significant statistically differed.