The sheath blight caused by the pathogen Rhizoctonia solani Kuhn is one of the most dangerous diseases of the cabbage seedlings. The disease affects the root system in the period from seedling emergence to complete formation of seedlings. In the absence of protective measures, sheath blight causes the mass premature death of plants. In order to provide healthy production of foodstuffs and reduce negative impact of chemical preparations on agrocnosises, the application of biological methods in the disease management is needed. Biological preparations are based on live antagonistic microorganisms, including fungi of the genus Trichoderma due to their great practical and environmental significance. Application of biological preparations reduces the infection of plants, increases resistance to a wide range of pathogenic microorganisms and improves the phytosanitary situation in agrocenosis. The aim of research work was to determine the influence of the liquid biological preparation Gliocladin-SC based on the fungus Trichoderma virens Miller, Giddens and Foster strain 3X, on the inhibition of the development of the pathogen Rhizoctonia solani, which causes sheath blight and on biometrics of cabbage seedlings, using the method of pre-sowing seed treatment. The antagonistic properties of the fungus T.virens 3X were studied in vitro against Rhizoctonia solani, by the method of colliding cultures in Petri dishes on agar nutrient medium (must-agar). Influence of the seed pre-treatment of the white early cabbage (var. Dittmarscher) seeds with biofungicide Gliocladin-SC in laboratory conditions in a greenhouse at a temperature 21–220C until the seed germination and at the temperature 16–170C after seedling emergence and with the 10-hour photoperiod has been studied. Before sowing, the seeds were treated with an aqueous suspension of the biological preparation in two concentrations: 1,5% and 5,0%. The control seeds were treated with water. The investigation of antagonistic activity of fungus T.virens, producer of biological preparation Gliocladin-SC, showed high inhibitory effect against the pathogen Rhizoctonia solani, causative agent of cabbage seedlings sheath blight. The antagonist inhibited mycelium growth and colonized pathogen, prevented the pseudo-sclerotia forming, demonstrating the mycoparasitic character of the antagonism. In the laboratory experiment using the method of seed pre-treatment , a stimulating effect of the aqueous suspension of biological preparation Gliocladin-SC for the development of the root system of cabbage seedlings has been found. The application of the 5,0% concentration of the biofungicide increased the root length of cabbage seedlings by 31,7% and the weight of the root system by 18,1% in comparison with control. Weight of the aerial part increased by 4,9% in comparison with control. The application of the 1,5% concentration of the biofungicide, increased the root length of cabbage seedlings by 31,5% and the weight of the root system by 6,0%. Application of biological preparation Gliocladin-SC for seed pre-treatment improves the quality of early cabbage seedlings.