Production of extracellular polysaccharides by moulds depends on culture conditions, including composition of growth medium, aeration and other parameters. These factors influence microbial physiology and therefore often increase or decrease yield of biosynthesis. Our article reports studies on scieroglucan biosynthesis by Sclerotium sp. strain from culture collection of Institute of Technical Biochemistry, Technical University of Lodz, under submerged culture conditions, focused on selection of a carbon source and an optimal C/N ratio, as well as on dynamics of scieroglucan biosynthesis dependently on a size of inoculum. During 7- days incubation we obtain from 1 litre of growth medium, 8.6 g of scieroglucan at specific productivity 1.7 gram/gram of biomass and 29% conversion of sucrose to scieroglucan.