During field experiments, we studied the dynamics of accumulation of various forms of carbohydrates in the seeds of four varieties of cultural soybeans, which differed in the level of photoperiodic sensitivity. Plants grew under the conditions of a natural long day (16 hours at the latitude of Kharkiv City, 50 0 N) and under the conditions of an artificial short day (9 hours). The carbohydrate content was determined at the stage of seed formation. Among all the varieties, regardless of their photoperiodic sensitivity, a short photoperiod stimulated the accumulation of carbohydrates in comparison with the accumulation in a natural long day. It is assumed that the process of formation of a set of carbohydrates in soybean seeds is subject to photoperiodic control.