Mangrove (Rhizophora mucronata) is a wetland plant that is widely found in South Kalimantan and is used as a diarrhea medicine, antidiabetic, inflammatory medicine, antiviral, anticancer, and body fitness enhancer. This study aims to determine the antioxidant activity of the graded fractionation of ethanol extract of R. mucronata leaves using the DPPH method, while the quantitative determination of antioxidant activity uses positive control of quercetin. The results of the antioxidant activity test of the n-hexane, ethyl acetate, and n-butanol fractions of R. mucronata were obtained at 77,0925 ppm; 52, 2873 ppm; and 25.2793 ppm. The results showed that the n-hexane and ethyl acetate fractions of R. mucronata leaves had strong antioxidant activity and the n-butanol fraction of R. mucronata leaves had very strong antioxidant activity.