The purposes of this study were to determine phenolic compounds and to evaluate antioxidant activities of plums (Soldam, Oishiwase and Formosa). Soldam contains the highest amount of total phenolics among cultivars (Formosa: 4.0%, Oishiwase: 3.3%, Soldam: 6.4% for total phenolic) as well as the total flavonoids of which constituents were mainly myricetin and anthocyanidin. The antioxidant activities were measured by DPPH, ABTS radical scavenging, and SOD-like activities. The DPPH radical scavenging activity of Korean plum extracts (200 ${mu}g/mL$) showed more than 43%, and the Soldam turned out to be the highest : ID50 value: 160-177 ${mu}g/mL$ for Formosa and Oishiwase; 58-64 ${mu}g/mL$ for Soldam. The ABTS radical scavenging activity of Korean plum extracts (200 ${mu}g/mL$) was found to be more than 50%. The SOD-like activity of Korean plum extracts (200 ${mu}g/mL$) showed more than 70%. Among three kinds of cultivars, Soldam had the highest antioxidant activity. The nitrite scavenging activity of Soldam was 61.5%, which is the highest, compared with that of the other cultivars, about 50%. From these results, Korean plums turned out to be phytochemical rich fruit as well as to show high antioxidant activities.