Aim. Find out the effect of different durations of the photoperiod on the protein and oil content in the seeds of soybean varieties, which differ in response to the photoperiod.Materials and methods. The experiments used photoperiodically neutral soybean varieties Annushka, Yatran, Ustya, as well as a short-day variety Khadzhibey. Plants were grown in the field 2016-2018 year at the experimental site of the Department of Physiology and Biochemistry of Plants and Microorganisms of V.N. Karazin Kharkiv National University on plots of 1 m2 in triplicate. From seedlings to the third true leaf, the plants grew with a natural long day (about 16 hours at the latitude of Kharkov - 50o N). In this phase, half of the plants were exposed to a short photoperiod for 14 days, darkening the plants with light-tight booths from 17 to 9 hours. After which the plants were grown again under long day conditions until the end of the growing season. The second part of the plants (control) during the entire growing season was grown under natural day conditions. The protein content in the seeds was determined on an infrared analyzer Infralum FT-10 (manufacturer Lumex, RF), according to the manufacturer's method, and oil - according to Rushkovsky. Analyzes were performed in two triplicate. The tables show the mean and standard deviations.Results. The protein content in seeds under the influence of a short photoperiod increased, decreased or did not change, compared with the content on a long day, regardless of the type of photoperiodic reaction of the studied varieties. The oil content in the seeds of all varieties, regardless of their photoperiodic reaction, exposed to a short photoperiod, as a rule, was lower than in the seeds of plants that were grown on a long day.Changes in the protein and oil content in the seeds of soybean varieties with different day lengths did not depend on the type of photoperiodic reaction.The content of both protein and oil in seeds varied in different varieties and in different years of research. The degree of variation in different varieties was different.Conclusions. Different photoperiodic conditions ambiguously influenced the protein content in the seeds of soybean varieties with different photoperiodic reactions, although in some years there was a tendency to increase it under the influence of a short photoperiod. Apparently, it is determined by the genotype of the variety and the meteorological conditions of the growing season.The oil content in the seeds of the studied varieties, which differ in the type of photoperiodic reaction, decreased under the influence of a short day, compared with the content under long day conditions.Apparently, the process of accumulation of protein and, especially, oil in soybean seeds is subject to photoperiodic control. Its mechanisms need in-depth studies at the level of physiological and biochemical processes.