This study investigated the biological activities of five benthic marine algae collected from Northeastern Region of Brazil. The tested activities included larvicidal activity against Aedes aegypti, molluscicidal activity against Biomphalaria glabrata, and toxicity against Artemia salina. Extracts of Ulva lactuca (Chlorophyta), Padina gymnospora, Sargassum vulgare (Phaeophyta), Hypnea musciformis, and Digenea simplex (Rhodophyta) were prepared using different solvents of increasing polarity, including dichloromethane, methanol, ethanol, and water. Of the extracts screened, the dichloromethane extracts of H. musciformis and P. gymnospora exhibited the highest activities and were subjected to bioassay-guided fractionation in hexane and chloroform. The chloroform fractions of the P. gymnospora and H. musciformis extracts showed molluscicidal activity at values below 40 μ g·mL(-1) (11.1460 μ g·mL(-1) and 25.8689 μ g·mL(-1), resp.), and the chloroform and hexane fractions of P. gymnospora showed larvicidal activity at values below 40 μ g·mL(-1) (29.018 μ g·mL(-1) and 17.230 μ g·mL(-1), resp.). The crude extracts were not toxic to A. salina, whereas the chloroform and hexane fractions of P. gymnospora (788.277 μ g·mL(-1) and 706.990 μ g·mL(-1)) showed moderate toxicity, indicating that the toxic compounds present in these algae are nonpolar.