Changes in antioxidant activity of Rubus coreanus fruit of 3 clones (S13, S114, and S16), which were selected from different sites, were studied at different ripening stages. Antioxidant activities (tree radical scavenging activity and reducing power) were determined and their relationships to total phenolic contents and ascorbic acid were analyzed. The highest tree radical scavenging activities of 3 clones (S13, S14, and S16) were 79.39, 75.80, and 81.16% at $125;{mu}g/mL$, respectively. In general, the antioxidant activity and the related parameters, including total phenolic content and vitamin C content decreased during fruit ripening. Total phenolic contents of the R. coreanus fruits (S13, S14, and S16) were correlated with tree radical scavenging activity ($R^2=0.8114$, 0.9186, and 0.9714). These results improve knowledge of the effect of ripening on the antioxidant activity and related compounds contents that could help to establish the optimum R. coreanus fruit harvest data for various usages.