Some plants have capacity as exogenous antioxidant. Simpor (Dillenia sp.) is plant of the Dilleniaceae family which may have the property of antioxidant. The purpose of this study was to measure the antioxidant capacity of the 96% ethanolic simpor leaf extract. Factorial design was applied with 2x3 factors of maseration time (24 and 48 hours) and concentration series of (10, 15, 20%). Normality was done by Kolmogorov-Smirnov and homogeneity by Levine. Data was analysed by ANOVA (ᾳ = 0.05). Post Hoc was analysed by Duncan. Antioxidant property was analysed qualitatively and quantitatively on flavonoid and also leaves water content. The antioxidant capacity assay was measured using DPPH (1,1-Diphenyl-2picryl Hidrazil) scavenging ability at 517 nm with ascorbic acid as control. The result showed that water content of the plant was 73.65%. Simpor contain flavonoids with highest flavonoid content (2.953 mg QE / mg) in 24 hours maceration time at 15% concentration. Furthermore, it also has ability to scavenge DPPH (1,1-Diphenyl-2picryl Hidrazil) radical with the highest value (97,10 ± 0,01%) in 24 and 48 hours maceration at 20% and 10% extract concentration. Statistical analysis on flavonoid content showed that time and concentration gave significant effect on flavonoid content (ᾳ = 0.003). Duncan result revealed that almost all groups didn’t significantly different only the 24 hours x 15% concentration was. DPPH inhibition based on statistic proved that both factors didn’t affect scavenging ability of Dillenia (ᾳ = 0.079). It can be concluded that simpor leaves has antioxidant capacity against DPPH radical due to its flavonoid content. Furthermore, concentration and maceration time significantly affect flavonoid content and didn’t affect DPPH radical scavenging ability of Dillenia plant.