This study investigated the yield and quality response of soybean [Glycine max (L.) Merr.] to full and deficit irrigation applied at different growth stages under sub-humid climate conditions over a two-year period. A rain-fed (non-irrigated) treatment and 13 different irrigation treatments (1 full and 12 deficit irrigations) were applied to soybeans at four critical development stages: vegetative (V), flowering (F), pod formation (P) and seed enlargement (S). Deficit irrigation had a significant effect on seed yield, crude oil content, crude protein content and various agronomic parameters. The highest seed yield (4004 kg ha(-1)) was obtained with full irrigation (based on the replenishment of 100% of soil water depletion from a soil depth of 90 cm at 7-day intervals throughout the development period) and the lowest (1974 kg ha(-1)) with the rain-fed treatment, with a 50.6% difference in average yield between full irrigation (VFPS) and rain-fed treatments. The rain-fed treatment also resulted in the lowest crude oil content (19.1%) and the highest crude protein content (33.6%). As a result, it may be concluded that while VFPS treatment may be the best choice for maximum yield under local conditions, irrigation schedules should be reconsidered when water cost is high and/or water is scarce; in such cases, an irrigation schedule that includes water deficit at the vegetative development stage can be applied.