In the present study, the effect of enzymatic hydrolysis on the antioxidant properties of whey protein isolate (WPI) was studied. Therefore, the whey protein solution was hydrolyzed for 5 h using alcalase enzyme. The antioxidant properties were measured using different methods including reducing power assay, DPPH radical scavenging test, and ABTS radical scavenging activity. The results showed that the enzymatic hydrolysis significantly (p < 0.05) increased the antioxidant activity of WPI and the resulting hydrolysates had better reducing power and free radical scavenging activity compared to the non-hydrolyzed counterpart. The results also showed that the highest level of antioxidant activity was related to the samples that were hydrolyzed for 5 h using alcalase enzyme and the lowest level of antioxidant activity was related to the native WPI. Therefore, the results of the present study suggested that the hydrolysates of WPI produced by action of the alcalase enzyme can be used as a natural antioxidant to replace synthetic antioxidants that have harmful effects on health, in various food formulations. The use of these antioxidant hydrolysates in food products can improve their health-related properties.