MARINE algae contain a variety of bioactive secondary metabolites and several compounds have been derived from them for prospective development of novel drugs by the pharmaceutical industries. In this laboratory experiment Cystoseira barbata was isolated from Red Sea coastal water (Safaga, Egypt). It was evaluated due to its bioactivities potential. Where the algal extract proved a potent activity against bacterial and fungal strains ranged between medium and high suppression action. It showed that Gram positive bacteria Bacillus subtilis and Staphylococcus aureus were more sensitive than Gram negative bacteria where Serratia marcescens, Pseudomonas aeuroginosa and fungus Candida albicans. Phyto-chemical analyses showed that C. barbata recorded the highest percentages of the flavonoids, phenols and saccharides compounds. Among the bioflavonoids determined Acacetin, Kaemp.3-(2-p-comaroyl) glucose, Rosmarinic and phenols were E-Vanillic, Benzoic and Ferulic were present in high percentages in the alga analyzed. The results indicated scope for utilizing this alga as a source of antibacterial and antifungal substances.