Ethyl acetate partition of methanol extracts of Avrainvillea nigricans. Decaisne (Udoteaceae), Codium decorticatum. (Woodward) Howe (Codiaceae), Halymenia floresia. (Clemente) C. Agardh (Grateloupiaceae), Laurencia obtusa. (Hudson) Lamouroux (Rhodomelaceae), Sargassum filipendula. C. Agardh (Sargassaceae), and Sargassum hystrix. J. Agardh, marine macroalgae from Yucatán peninsula coasts, were screened using the well-diffusion technique against three Gram-positive bacteria, four Gram-negative bacteria, two yeasts, and two molds. The extracts inhibited the growth of Staphyloccocus aureus. at 6.25–1.56 mg/mL and Bacillus subtilis. at 6.25–0.78 mg/mL. Trichophyton mentagrophytes. growth was inhibited by extracts of Laurencia obtusa., Sargassum filipendula., and Sargassum hystrix. at 6.25–3.13 mg/mL. The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and minimum fungicidal concentration (MFC) were obtained by the microplate method.