Background: Immature fruit of Rubus coreanus, also known as “Bokbunja” in Korea, have been used as traditional medicinal plant in East-Asia. Although several studies have been conducted to the fruit composition of R. coreanus, research on the antioxidant composition of branch and leaves are limited. Objectives: We aimed to analyze the contents of five antioxidants in leaves and branches of R. coreanus using different extraction method. Materials and Methods: R. coreanus were cultivated at the research farm of the Gyeongsang National University. R. coreanus plants were harvested in May and July, and leaf and branch extracts were prepared using the ultrasonic bath and reflux extraction methods and analyzed using liquid chromatography-tandem mass spectrometry. Results: The ultrasonic bath extraction method extracted 7.1 and 1.5 mg/100 g gallic acid from leaves and branches, respectively, whereas the reflux extraction method yielded 12.4 and 16.5 mg/100 g, respectively. Thus, reflux extraction was superior to ultrasonic bath for both leaf and branch parts. In the extracts prepared by reflux extraction, contents of all five compounds were higher in leaves than in branches. In leaves extracted with the reflux extraction method, ellagic acid was the most abundant, followed by quercetin-3-O-glucoside (24.7 mg/100 g), gallic acid (12.4 mg/100 g), quercetin (7.3 mg/100 g), and kaempferol (1.5 mg/100 g). Contents of all compounds were higher in May (1.1 mg/g) than in July (0.7 mg/g). Conclusion: R. coreanus plant was identified to show antioxidant activity and to present abundantly five antioxidants not only in fruit but also in leaves and branches in May. Specially, quercetin was three-fold higher in leaves than in fruit juice.