Abstract: Indonesia is a biodiversity rich country. Mistletoe is one of the unique Indonesian biodiversity. As a semi-parasitic plant, mistletoe is considers as an unwanted plant to economically important horticultural plant, however in the other side, mistletoe is known as one of medicinal plant used in traditional therapy. Mistletoe potency as drug material should be studied so the utilization of mistletoe could be developed. Compare to mistletoe that grown on tea as the host plant, relatively less studies are conducted in mistletoe that grown on other host plants, although it was reported the species of host plant could affected the chemical constituents in the mistletoe. Previous study shows that the antioxidant activity (based on measurement using DPPH free radical scavenger method) of leaf extracts of mistletoe (Dendrophthoe pentandra) that grown on star fruit (Averrhoa carambola) were depend on the solvent used for extraction. In this study we reported antioxidant activity guided isolation of chemical constituent from ethanol extract of this mistletoe leaves. Separation was conducting using vacuum column chromatography and characterization was conducted using TLC, LC-MS, UV-VIS and IR spectrophotometer and melting point apparatus. From the results obtained it was suggest that the isolated compound is a flavonol glycoside, quercitrin (quercetin-3-O-rhamnoside) which an active antioxidant with IC50 value of 5.19 μg mL-1.