In recent years, interest in biologically active substances from cyanobacteria has increased. The ability to improve immunity as well as the property of suppressing the activity of various fungal, bacteria and viruses in humans and animals has shown that the cyanobacterium Spirulina (Arthrospira) platensis and various extracts from its biomass (especially phycobiliproteins, carotenoids, phenolic compounds, flavonoids, acid polysaccharides etc.) can be successfully recommended in the development of new preventive remedies and alternative sources of antiviral, antimicrobial, antifungal agents [1-4]. The emergence of new strains of viruses, bacteria, fungi, as well as the increase in their resistance to drugs, raises the interest of researchers for finding of new natural antibacterial, antiviral, antifungal sources as an alternative to synthetic drugs. In our research it was established that the extract with polysaccharide content obtained from the biomass of Spirulina platensis grown in the presence of zinc acetate showed microbiostatic and microbicidal action on both gram-positive and gram-negative bacteria and yeast fungi of the genus Candida. Higher activity this extract demonstrated on the strains of Bacillus cereus ATCC 11778 and Acinetobacter baumannii ATCC BAA-747, demonstrating bacteriostatic effect in 1: 1 dilution and bactericidal efect in 1: 2 dilution. On the bacteria Escherichia coli ATCC 25922 this compound did not show bactericidal effect, only bacteriostatic effect in 1: 1 dilution. This compound also demonstrated a fungicidal and fungistatic effect on yeast fungi Candida albicans ATCC 10231 in a 1: 1 dilution. Thanks to its valuable biochemical composition, Spirulina platensis may be exploited as potent natural sources of nutraceutical and functional ingredients and can be widely used in animal feed and food supplement, pharmaceutical and health protection industry including as a preventive and alternative remedy, as well as a source of antiviral, antibacterial, antifungal agents.