Introduction of sprouted soybean grain into animal diet provides high protein content in feed, increases its nutrition and digestibility. In the technology of preparation of green vitamin forages based on soybean for seed disinfection before sprouting it is proposed to use UV-irradiation. In order to determine the optimal modes of seed pre-sowing treatment according to the presented methodology, UV-irradiation of soybean seeds was carried out on the previously developed experimental unit of belt type. The treated seeds germinated in a closed box with forced ventilation and a built-in phytolamp. The energy illuminance of UV irradiation and the time of UV treatment of seeds before sprouting were selected as the variable factors, and the length of soybean sprouts on the 5th day of sprouting was selected as the response function. The regression equation describing the influence of UV-treatment parameters on sprout length was obtained from experimental data, and graphical dependences of the response function changes in the variation intervals were plotted. Experimental studies have established the optimal mode of UV-treatment of soybean seeds, providing the maximum value of soybean sprouts. At a specific power of 9 W/m2 with UV-irradiation exposure from 30 to 90 s the length of sprouts on the 5th day of sprouting was 120 mm (with 109 mm in control samples). The proposed mode is recommended for pre-sowing seed treatment during sprouting of soybean seeds for vitamin feed for animals.