Abstract: Whey oligopeptides were prepared by the method of two-step enzymolysis.The compositions, amino acid composition and molecular weight distribution of whey oligopeptides were determined.Antioxidant activities of whey oligopeptides were evaluated from four aspects by determination of the scavenging activities against hydroxyl radical, superoxide radical and DPPH radical as well as reducing power.Composition analysis indicated that the content of total protein was 86.83% and the amino acids were abundant. Whey oligopeptides were rich in antioxidative amino acids, in which leucine, valine and proline were dominated.The major molecular weight of whey oligopeptides was less than 1000u ( 85.78%) , and the peptides with a molecular weight range of 132 ~576u were59.55%. Results of antioxidant tests showed whey oligopeptides exhibited antioxidant activities and the antioxidant activities showed a dose- response relationship with the concentration. The half inhibitory concentrations ( IC50values) of hydroxyl radical and DPPH radical scavenging activities were 2.3 and 4.2mg /mL, respectively.And the reducing power of whey oligopeptides at 2.5mg /mL was identical with that of ascorbic acid at 0.012 mg /mL.