The present study aims to determine the chemical composition, nutritional value, bioactive compounds content and biological activities of the brown alga (Sargassum subrepandum) collected from the Mediterranean Sea coasts, Egypt. Data of proximate chemical composition of Sargassum subrepandum powder indicated that carbohydrates were the largest compound (59.68 ± 3.23%) followed by ash (16.23 ± 1.14 %), crude fiber (9.18 ± 2.02 %), total protein (4.98 ±0.61%) and crude fat (0.91 ± 0.12%.). Also, the total energy Kcal/100g, G.D.R. (g) for protein (63 g) and G.D.R. (g) for energy (2900 Kcal) for the same samples were 266.83± 4.73, 1265.06±20.67g and 1086.83±15.48, respectively. Furthermore, bioactive compounds content of Sargassum subrepandum powder indicated that polysaccharides were the largest compound (152.45± 19.32 mg starch equivalent. g-1) followed by phenolics (122.67 ± 20.34 mg gallic acid equivalent. g-1), tannins (34.15 ± 6.90 mg catechin equivalent. g-1), carotenoids (30.78± 6.41 mg. g-1), flavonoids (29.31 ± 5.67 mg catechin equivalent. g-1) and anthocyanin's (3.65± 0.44 mg Cyanidin 3-glucoside, CCy3G equivalent.100g-1). The samples also recorded several very high biological activities which include inhibition of low-density lipoprotein (LDL) oxidation, scavenging of free radicals, and antibacterial and antifungal. Such important biological effects could play important roles in strategies to combat/treat many diseases, especially those for which oxidative stress is one of the mechanisms for its occurrence i.e. diabetes, cancer, atherosclerosis, etc. Therefore, the present study recommended that brown alga (Sargassum subrepandum) powder and/or extracts to be included in our daily diets, drinks, food supplementation and pharmacological formulae.