This study evaluates the feasibility of using sub-critical water extraction (SWE) processes to obtain antioxidant phenolic compounds from peanut skins. Theoretical models were tested against experimental data in order to optimize extraction conditions and antioxidant activity of target compounds. The maximum concentration of total phenolics was achieved by using 60.5% ethanol as co-solvent, at 220 degrees C extraction temperature and 7 g/min solvent flow. Under these extraction conditions, a large number and variety of polyphenols were identified. Phenolic profile was dominated largely by monomeric and condensed flavonoids, particularly procyanidin and proanthocyanidin oligomers. Extracts obtained under those conditions also gave the best radical scavenging capacities, which were higher to those reached by using a synthetic antioxidant (BHT, butylhydroxytoluene). Kinetic studies showed a high extraction rate of polyphenols until the first 30 min of extraction, and it was in parallel with the highest antioxidant activity.