In the present study, a quantitative and qualitative comparison of major flavonoids and phenolic components of 6 species of Mediterranean Sea seaweeds collected from Stanley to Abu Qir Bay, Alexandria, Egypt (Enteromorpha intestinalis, Ulva lactuca, Punctaria plantaginea, Colpomenia sinuosea, Dictyota dichotoma and Corallina officinalis) were carried out using HPLC instrument. Also, the chemical profile of the non-polar components extracted by the petroleum ether solvent of these species was identified using GC-MS technique. n-hexadecanoic acid (8) was identified in all petrolum ether extracts (p1-p6) recording 18.0%, 17.2%, 17.2%, 20.2%, 19.2% and 16.8% for E. intestinalis, U. lactuca, P. plantaginea, C. sinuosea, D. dichotoma and C.officinalis (p1-p6), respectively. The antimicrobial activity of the obtained extracts was evaluated and E. intestinalis crude extract (M1) was the effective antimicrobial agent. Total phenolic and flavonoid contents were also evaluated for the selected six Mediterranean Sea seaweeds species. D. dichotoma and C. officinalis recorded the highest phenolic and flavonoid contents among all selected species, 31.42 mg/g, 23.42 mg/g for phenolic and 173.9 mg/g, 165.4 mg/g for flavonoid, respectively. These findings are compatible with HPLC analyses as D. dichotoma contains eight flavonoids and eleven phenolic constituents, in addition to C. officinalis also contains eight flavonoids and ten phenolic compounds.