In France and Indonesia, Sargassum is quite abundant yet this alga has not been optimally exploited. Sargassum contains macro and micro molecules and also bioactive compounds, the most known is phlorotannins, showing a wide range of pharmacological properties. Therefore, it is interesting to further valorize this alga for various industrial applications, such as food, pharmacology and cosmetic. Knowledge on biochemical composition of this alga, which also represents its nutritive value, is essential for food industries. Concerning the bioactive compound, solid-liquid extraction is the most commonly used technique in the extraction of phlorotannins from brown algal biomass. However, phlorotannins of brown algae are known to be bound with algal cell wall and the high content of various cell wall polysaccharides in macroalgae limit the active compound accessibility. Thus, these cell walls strongly reduced the extraction efficiency application of conventional extraction. As a consequence, it is important to consider the degradation of algal cell wall as a way to liberate more phlorotannins. Application of enzymes is considered as one process that might facilitate the degradation of algal cell wall leading to the recovery of phlorotannins from brown algae.This study had three main subjects of interest; they were (1) the characterization of Sargassum biochemical composition and its seasonal variation, (2) solid-liquid extraction and (3) enzyme-assisted extraction of Sargassum phlorotannins and their bioactivities. The bioactivities analyzed in this study included antioxidant (DPPH radical scavenging and FRAP reducing power), antibacterial, tyrosinase, elastase, biofilm inhibition, cytotoxicity and antiviral activity.In this study, minerals represented a significant value with a content reaching 33% followed by proteins with 24% of algal dry material. In the contrary, sugars showed only 13% of algal dry material. The study of seasonal variability demonstrated that the biochemical composition of Sargassum, as for most algae, is strongly affected by the season and it appears to be related to the life cycle of the algae. Same cases happened with the polyphenol compound of Sargassum.Nevertheless, suitable extraction method is important to choose in order to increase the yield. Solid-liquid extraction yielded lower (5-24% of algal dry material) compared to enzyme-assisted solid-liquid extraction (21-38% of algal dry material). Regarding the polyphenol content, enzyme-assisted extraction also yielded a better yield, 32%, compared to 26% of algal dry material if the extraction is carried out without enzyme.After the screening of eight enzymes to extract the polyphenols from S. muticum, Viscozyme - a cellulase, released a greater quantity of phenolic compounds according to Folin Ciocalteu method, result was also confirmed by the anti-free radical activity of (IC50 0.6 ± 0.1 mg mL-1). This extract also managed toprevent 43.7 ± 4.2%, higher than the other extracts, of biofilm formation generated by P. aeruginosa.Other than antiradical activity, it seems that each enzyme showed different potential. In reducing power, the most important activity was shown by AMG (an exo-amylase) extract (60.8 ± 1.8 μM of Fe2+). Ultraflo (a xylanase) extract had promising potential in inhibiting the tyrosinase at 24.5 ± 2.6%, while Shearzyme (cellulose and xylanase) extract showed higher inhibition elastase activity than the other extracts, 30.9 ± 5.9%. Viscozyme extract was able to hamper 43.7 ± 4.2% of film formation generated by P. aeruginosa. However, Shearzyme extracts exhibited strong biofilm inhibition activity against the E. coli, 60.3 ± 10.3% of inhibition.The application of enzymes in the extraction of the Sargassum phenolic compound is quite effective. In addition, Sargassum enzyme extracts demonstrate a wide range of bioactivity. It is important to consider that, using enzymes, the phenolic compound is probably not the only compound extracted from the algal matrix by the enzymes. As a result, it will be interesting to continue working on the purified samples pretreated by enzyme-assisted extraction in the future. In addition, the characterization of the Sargassum phenolic compound could help to better understand the mechanisms of their bioactivity.