SOME mycological strains have been reported to be resistant to commonly used drugs. As a result, the development of new and important antifungal drugs has become a global endeavor. This study investigated the antifungal activity of three brown marine macroalgae, Sargassum cinereum, Padina boergesenii, and Cystoseira myrica against three fungal dermatophytes, namely Candida albicans, Candida glabrata, and Candida tropicalis and two nondermatophytic, Fusarium oxysporum and Alternaria alternata using the disc diffusion assay. Algal extraction was performed using three organic solvents (acetone, ethanol, and methanol). The results showed that the seaweed extracts exhibited different patterns of antifungal activities. The ethanolic extract of Sargassum cinereum was the most active as compared to other organic extracts. The maximum antifungal activity of the S. cinereum ethanolic extract was 21.3 ± 0.32 and 18.8 ± 0.16mm against F. oxysporum and C. glabrata, respectively, followed by the methanolic extract of C. myrica (16.5 ± 0.21mm) against F. oxysporum, and ethanolic extract of P. boergesenii (16.3 ± 0.16mm) against C. glabrata. The minimal inhibitory concentrations (MICs) of the algal extracts for inhibiting the tested fungi were in a range of 8.5–70μg/mL. The ethanolic extract of S. cinereum had the lowest MIC value (8.5 ± 0.12μg/mL) against F. oxysporum. The gas chromatography–mass spectrometry of the ethanolic extracts revealed the presence of chemical constituents that could have significant antifungal effects in the brown marine macroalgae. The main constituents were the hexadecanoic acid methyl ester (palmitic acid); 3,7-dimethylocta-2,6-dienal; and octadecanoic acid methyl ester.