MARINE macroalgae are considered as a promising source of chemical compounds with a broad array of biological activities. The bioactive compounds of five marine seaweeds (Ulva lactuca, Padina boryana, Cystoseira myrica, Liagora farinosa and Acanthophora spicifera) were extracted by chloroform, dichloromethane and ethanol. We managed to extract two polyphenolic compounds (ellagic acid and velutin) from the dichloromethane extract of P. boryana and ethanol extract of A. spicifera, respectively. The biological activities of the two isolated compounds as well as the crude extracts were screened. All tested algal extracts showed high antimicrobial activity against target bacteria and fungi except for Pseudomonas aeruginosa was resistant to U. lactuca and C. myrica extracts. Chloroform and ethanol extracts of A. spicifera, and dichloromethane extract of C. myrica showed the highest antimicrobial activity against Bacillus subtilis and Staphylococcus aureus. Dichloromethane extract of P. boryana had the highest antiprotozoal activity against Trypanosoma cruzi and Leishmania donovani (IC50 values, 3.5 and 4.8 μg/mL, respectively), and potent antioxidant activity up to 60 %. Overall, marine macroalgae with high polyphenols and flavonoids content exhibited excellent antimicrobial, antiprotozoal and antioxidant properties. Purified velutin recorded high antimicrobial activities as compared to the tested antibiotics and both ellagic acid and velutin also possessed considerable antiprotozoal activities. This study suggests that, ellagic acid and velutin comprise the key players for the antimicrobial and antiprotozoal activities of P. boryana and A. spicifera extracts, respectively. Thus, these two compounds could be used as pharmaceutically bioactive natural compounds.