Seaweeds are recognized as valuable sources of nutrition. Among them, the red seaweeds Grateloupia turuturu and Porphyra umbilicalis are particularly noteworthy, commonly consumed as food in East Asia, and known for their unique bioactive compounds. Nonetheless, knowledge gaps remain in studies on their phytochemical composition and bioactivities. Hence, G. turuturu and P. umbilicalis hydroethanolic and aqueous (infusion and decoction) extracts were prepared to first characterize their reducing compounds. Then, the cytotoxicity of the seaweed extracts was evaluated in RAW 264.7 cells. Antioxidant activity was then assessed in three biochemical assays (ABTS^•+, ^•OH and ^•NO radical), and anti-inflammatory potential was measured in RAW 264.7 cells. Folin—Ciocalteau results showed a higher content in reducing compounds for aqueous extracts compared to hydroethanolic extracts for both seaweeds. RP-HPLC-DAD/LC-DAD-ESI-MS analyses showed the presence of myscoporine-like amino acids (MAAs), but not phenolics. P. umbilicalis had a higher MAA content than G. turuturu across all extracts, with porphyra-334 being the most concentrated MAA in P. umbilicalis and shinorine in G. turuturu. The highest carbohydrate content (39% extract) was shown by P. umbilicalis decoction. For cytotoxicity upon 24h exposure, a P. umbilicalis infusion extract had an IC₅₀ of 0.43 mg/mL, while other extracts showed IC₅₀ values above 0.75 mg/mL. G. turuturu and P. umbilicalis decoction extracts showed the highest ABTS^•+ scavenging, at 70 and 97 mmol TE/g extract, respectively. G. turuturu water extracts produced the highest scavenging against ^•NO, 54-56%, while both hydroethanolic extracts exhibited the highest ^•OH scavenging (55%). All seaweed extracts inhibited NO production/release in lipopolysaccharide-induced cells, with the highest anti-inflammatory activity shown in P. umbilicalis hydroethanolic extract, reducing NO levels to 41%. MAAs and carbohydrates are believed to be the main compounds accountable for the bioactivities. Thus, G. turuturu and P. umbilicalis reinforced their potential as nutraceuticals and sources of bioactive compounds.