Today, there is a debate between scientists on the toxicity of ZnO nanoparticles, which are often used in food, cosmetological and pharmaceutical industries. Some researches show that only nanoparticles smaller than 30 nm are toxic, other researches showed that nanoparticles are toxic to living organisms regardless their size. It is known that carbohydrates perform a number of functions in the cell. Thus, they serve as reserve substances, participate in the transport of nutrients, ensure the correct structure and protection of cell membranes and, in complex with other substances, regulate the synthesis of different substances, cell growth and its multiplication. Stimulation of carbohydrate biosynthesis usually occurs in response to various unfavorable cultivation conditions, such as suboptimal temperatures, high osmotic pressure, deficiency in nutritional sources, presence of various harmful substances in the nutrient medium, and indicates to a probable stress state of the microbial cells. In this context, the aim of the research was to evaluate the effect of ZnO nanoparticles with <100 nm size on biomass production and carbohydrate content of Saccharomyces cerevisiae CNMN-Y-20 yeast strain, a β-glucans active producer, deposited in the National Collection of Nonpathogenic Microorganisms. There were used ZnO nanoparticles in powder form ALDRICH, dispersed in poly(Nvinylpyrrolidon) in concentrations of 0,5; 1; 5; 10 and 15 mg/L. The nanoparticles were added as an emulsion in YPD culture medium at the time of inoculation with the seed material. As a control was examined variant without nanoparticles. The yeast biomass was collected by centrifugation after 120 hours of cultivation. Total carbohydrate content was also determined after 120 hours. The obtained results demonstrate that biomass amount presented a relative stability for the yeast strain cultivated in the presence of <100 nm ZnO nanoparticles (Figure). Its content, calculated on 1L culture medium, varied practically at the control level. The influence of ZnO nanoparticles (<100 nm) on total carbohydrate content has revealed different values depending on the concentration of used nanoparticles. The results showed an increasing tendency of their content in the presence of nanoparticles in 1-15 mg/L concentrations. Thus, carbohydrate content was up to 16.5% higher than control (Figure). Therefore, the results denote that the effect of ZnO nanoparticles (<100 nm) depends on their concentration in culture medium. Namely, ZnO nanoparticles in concentrations of 1-5 mg/L have been manifested as stimulators of carbohydrate biosynthesis in S. cerevisiae CNMN-Y-20 strain.