The growing trend toward natural products in pharmaceuticals has fueled a surge in interest for exploring bioactive compounds from marine algae. Phenolic compounds, a vast and ubiquitous class of plant chemicals, have become a major focus of research due to their diverse pharmacological properties and potential health benefits. Seaweeds hold an immense potential due to their vast array of versatile molecules with diverse properties and multiple biological activities. Three algal samples from the Chlorophyta (Ulva lactuca), Phaeophyta (Sargassum vulgare) and Rhodophyta (Corallina officinalis) were assessed for phenolic compounds content and antioxidant power, in addition of a chemical characterization of the most active fractions using RP-HPLC technique. Fifteen extracts were obtained and phenolics and flavonoids were quantified. C. officinalis ethyle acetate and butanolic fractions were the most potent extracts. Gallic, chlorogenic, and p-coumaric acids were identified in the both extracts in addition to rutin, catechin and naringenin compounds. Our findings highlighted the significant potential of C. officinalis as a powerful alga tested. Future research will delve deeper into this promising species to fully explore its bioactive potential.