Abstract: The antioxidant capacity of aqueous soluble extract with small molecules of Three- spot hippocampus was investigated.Three- spot seahorse was taken as raw material,extracts were obtained via reflux extraction using95% ethanol and systematic solvent extraction. Aqueous extract was selected for further analysis amongst the resulted various polar extracts. Six fractions were obtained by eluting through Sephadex G- 10 gel filtration chromatography.Anti- oxidative activities of DPPH free radical scavenging,and hydroxyl radical scavenging,total reducing power and ferrous ion chelating ability were determined and evaluated at multiple concentrations and total polyphenols and total amino acids of varying fractions. The results indicated: by contrast,DPPH free radical clearance of Fr Ⅳ was the highest with the of IC₅₀ of 0.25 mg / m L. Total reducing power FrⅣ was potent,Fr Ⅳexhibited the highest capacity for scavenging hydroxyl radical and ferrous ion chelating ability. Collectively,the antioxidant activity of aqueous soluble extract with small molecules of Three- spot hippocampus seemed to have correlation with the distinct contents and types of phenolic compounds,amino acids,small molecular peptides.