The aim of the thesis is to determine the antifungal effect of extracts of marine organisms, the mantle Aplydium conicum, the green macroalgae Codium bursa, the brown macroalgae Cystoseira compressa and coral Eunicella cavolinii. The extracts were prepared in water for polar and dimethylsulfoxide for non- polar components to compare their action. Antifungal testing was performed on the most important mycotoxicogenic molds: Alternaria alternata, Aspergillus flavus, Aspergillus ochraceus, Fusarium gramniearum, Fusarium verticillioides, and Penicillium expansum by a standardized microdilution method according to the CLSI M38-A guide. According to the results obtained, it was observed that extracts of all marine organisms had an inhibitory effect on certain mold species at certain concentrations. Excellent inhibition effects - MIC\(_{50}\) 5 μg/mL, were shown by the aqueous extract of Cystoseira compressa for Aspergilus flavus mold and the DMSO Eucinella extract for Alternaria alternate mold. In general, the best antifungal activity was demonstrated by Codium bursa algae extracts, which inhibited all the mold species used. The influence of extracts on the growth of molds - GIC\(_{50}\) was also investigated, where it was observed that 4 extracts had a stimulating effect on the growth of Aspergillus flavus already at concentration of 5 μg/mL - Codium bursa algae extract and DMSO extracts of macroalgae Cystoseira compressa and coral Eucinella cavolinii.