The potential antioxidative activity of water-soluble enzymatic hydrolyzates from a kelp, Ecklonia cava was evaluated by free radical scavenging and lipid peroxidation assays. To prepare water-soluble hydrolyzates from E. cava the seaweed was enzymatically hydrolyzed by five carbohydrases (Viscozyme, Celluclast, AMG, Termamyl and Ultraflo) and five proteases (Protamex, Kojizyme, Neutrase, Flavourzyme and Alcalase). Among all the hydrolyzates, Celluclast hydrolyzate effectively scavenged free radicals released from DPPH (1,1-diphenyl-2- pricrylhydrazyl) and recorded around 73% scavenging activity at the concentration of 4 mg ${cdot}ml^{-1}$. This hydrolyzate was thermally stable and DPPH radical scavenging activity remained 80% or higher at heating temperatures of 40 and 60$^{circ}C$ up to 12 h and around 80% at 100$^{circ}C$ up to 8 h. AMG and Ultraflo hydrolyzate inhibited the lipid peroxidation of fish oil as that of $alpha$-tocopherol. These results suggested that an enzymatic extraction will be an effective way for the production of a potential antioxidant from seaweeds.