This study aimed to optimize the extraction conditions for a valuable source of antioxidants: seaweed. Therefore, ten seaweed samples were subjected to a solid-liquid extraction (SLE), where the extraction conditions (biomass (g): solvent (mL) ratio, temperature, and time) were optimized using response surface methodology (RSM). The seaweeds were also subjected to subcritical water extraction (SWE) (140 and 190 °C) and ultrasound-assisted extraction (UAE) (10 and 20 min). The antioxidant capacity of the extracts was determined through the ferric-reducing antioxidant power and the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid). The total phenolic content revealed the significance of temperature and biomass
solvent ratio parameters in the extraction process with higher conditions generally promoting the release of phenolic compounds. Furthermore, applying RSM allowed for the identification of optimal conditions and the establishment of predictive models that can be valuable in industrial-scale extraction processes. The antioxidant potency composite index (APCI) shows that SWE at 190 °C stands out, with