Abstract: Background and Objective: The addition of ‘jamblang’ peel could increase the beneficial properties of ‘Kolang-kaling’ jam, including antioxidant activity. This study was conducted to evaluate the effect of ‘jamblang’ peel and citric acid addition on the antioxidant activity of ‘Kolang-kaling’ jam. Materials and Methods: A factorial design with a completely randomized design that considered 2 factors was used. Factor A was addition of ‘jamblang’ peel, at four concentrations: A1 (10%), A2 (15%), A3 (20%) and A4 (25%) and factor B was the addition of citric acid at three concentrations: B1 (0.2 g), B2 (0.3 g) and B3 (0.4 g). ‘Kolang-kaling’ jam with the various additions was analyzed for total phenol and total anthocyanin content, as well as antioxidant activity (IC50). Results: The addition of ‘jamblang’ peel and citric acid significantly (p<0.05) and synergistically (p<0.05) increased the total phenol and anthocyanin content of ‘Kolang-kaling’ jam in a dose-dependent manner. Meanwhile, the IC50 of the jam dose-dependently decreased with ‘jamblang’ peel and citric acid addition and was negatively correlated with total phenol content (r = -0.881) and anthocyanin levels (r = -0.683). Conclusion: The highest antioxidant activity, (1,376 ppm) was seen in jam production with 25% ‘jamblang’ peel and 0.4 g citric acid. Anthocyanin had a stronger effect on antioxidant activity than did citric acid. Although the antioxidant activity in ‘Kolang-kaling’ jam was relatively weak even with ‘jamblang’ peel and citric acid supplementation, this food still could be used as an antioxidant substance.