Abstract: Rice oligopeptides were prepared from rice protein powder by two-step enzymatic hydrolysis.Based on the analysis of their basic physical and chemical components，the structure of rice oligopeptides was characterized by amino acid composition，relative molecular weight distribution，scanning electron microscopy，ultraviolet spectrum  and circular dichroism.The in vitro antioxidant activity of rice oligopeptides was investigated by four index of in vitro antioxidant evaluation system including hydroxyl radical scavenging ability，ferric ion reducing antioxidant power （FRAP），oxygen radical absorbance capacity （ORAC） and reduction capacity.The results show that： the protein and peptide contents in rice oligopeptides are 95.75%±0.53% and 89.11%±0.94%；rice oligopeptides are rich in antioxidant amino acids such as leucine，alanine and valine，and the components with relative molecular weight less than 1000 accounted for 91.84%；rice oligopeptides are obvious spherical granules，and have irregular folds and pores on the surface；the maximum absorption peak appears at 270 nm wavelength；the contents of α-helix，parallel β-fold，antiparallel β-fold，β-turn and random coil are 6.0%±0.3%，3.3%±0.2%，40.2%±1.9%，19.5%±1.0%，and 32.1%±2.5%，respectively.The IC50 value of rice oligopeptides to hydroxyl free radical is about 11.1g/L，and ORAC value is （498.88±18.29） μmol/g （with Trolox as the standard）；the FRAP value of rice oligopeptides at 15.0g/L is equivalent to that of 0.04g/L positive control Vc，and the redu-cing ability of rice oligopeptides at 15.0g/L is equivalent to that of 0.05g/L Vc. 

Key words: rice oligopeptides, structure characterization, antioxidant activity, enzymolysis