In the present work, three macroalgae viz; Halimeda tuna, Padina gymnospora and Phacelocarpus tristichus, collected from Egyptian Red Sea shores were investigated for their chemical composition and pharmacological properties. Volatile compounds of 70% methanol extracts of three selected algae were analyzed by GC-MS. Antimicrobial and cytotoxic activities of algal extracts (70% methanol) were tested by agar well diffusion and in vitro cell viability assays, respectively. P. gymnospora showed the maximum antibacterial activity against E. coli (13.90±0.66 mm), followed by P. tristichus (12.97± 0.65mm), while H. tuna inhibited significantly the growth of S. aureus (13.17± 0.67mm). Furthermore, the highest antifungal activity was obtained by P. gymnospora, followed by P. tristichus and finally H. tuna against C. neoformas and A. fumigatus. Also,P. gymnospora showed more cytotoxicity against HepG-2 and MCF-7 cell lines than P. tristichus and H. tuna. Moreover, it is the first report of chemical composition, antimicrobial activity and cytotoxicity of P. tristichus and also this research showed new reports on cytotoxicity of P. gymnospora and H. tuna against new cell lines. In conclusion, the Egyptian marine macroalgae possess antimicrobial and cytotoxic activities, that could be investigated for future application in medicine and recognizing novel drugs from the marine resources after checking their bioavailability in vivo.