Aim. The aim of the work was to elucidate the influence of photoperiod duration on the dynamics of the fruits and seeds formation in soybean varieties with different photoperiodic reactions. Methods. The field experiments were carried out by cultivating soybean varieties Anushka, Ustia, Yatran and Hadzhibey under the conditions of a long natural day (16 hours) and an artificially short day (9 hours). Phenological observations and morphometric analyzes wee used. Results. The varieties Annushka, Ustya and Yatran showed a photoperiodic neutral reaction to the photoperiod and Hadzhibey – a short reaction. In all varieties, regardless of the photoperiodic reaction, a short photoperiod accelerated the formation of fruits and seeds. In the greatest degree, this was shown for the short-day variety Hadzhibey. Conclusions. The formation of fruits and seeds in soybean is subjected to photoperiodic regulation, probably due to the change of intensity of its supply of assimilation products under the influence of different day lengths.Keywords: soybean, (Glycine max (L.) Merr.), photoperiod, rate of development, photoperiodic reaction, fruits, seeds.