Nutritional composition, total Phenolic content, antioxidant and antimicrobial activities were assessed in the crude extracts of six seaweed species selected from the Red Sea coast, Hurghada, Egypt. These species are Caulerpa racemosa var. gracilis from Chlorophyta; Padina boergesenii, Polycladia myrica, Hormophysa cuneiformis and Sargassum aquifolium from Phaeophyta and Digenea simplex from Rhodophyta. The results of nutritional content revealed that, the tested seaweeds have high values of fibers (27.6-36.2% dry wt.), ash (24.7–35.8% dry wt.), and carbohydrates (23.4-35.7% dry wt.), medium values of moisture (2.4-10.8% dry wt.) and protein (4.8-7.1% dry wt.), while low values of total lipids (0.8-5.2% dry wt.) were detected.  The highest total phenolic content (129.9 ± 1.8 mg GAE/g dry wt.) was detected in the brown seaweed, H. cuneiformis, and the lowest (31.3 ± 0.6 mg GAE/g dry wt.) was observed in the green seaweed C. racemosa. The antioxidant activity was detected using DPPH (2, 2-Diphenyl-2-picrylhydrazyl) radical scavenging activity and the highest activity was recorded in the brown seaweed H. cuneiformis, while the lowest activity was observed in the green seaweed C. racemosa. All the algal extracts were effective against Pseudomonas aeruginosa and Candida albicans, while the extract of H. cuneiformis is the only one that effective against Enterococcus faecalis and Staphylococcus aureus. None of the tested extracts was effective against Aspergillus niger. Overall, the results of this study indicated that the Red Sea seaweeds could be introduced as raw materials or some of their contents for nutrient supplementation in various food products.