Degenerative diseases such as cancer, heart disease is one of the diseases caused by free radicals. Dengen (Dillenia serrata) is one of Indonesia's endemic local plants that has the potential to bind free radicals. So far, only limited to the use of fruit and consumed directly. This study aims to determine the ability of dengen stem bark extract to bind to free radicals expressed in IC 50. In the initial research, the total content of polyphenols in dengen stem bark extract was 444.8 mg GAE/g or 44.48%. Dengen stem bark is extracted by maceration using 70% ethanol solvent. Antioxidant activity was calculated based on IC 50 (Inhibition Concentration) values using the DPPH method, and measured at a wavelength of 516 nm. Ethanol extract of dengen bark is made in 5 concentration series, namely 10 ppm, 20 ppm, 30 ppm, 40 ppm and 50 ppm. Ethanol extract of dengen bark has a very active antioxidant activity with an IC 50 value of 48.33 ppm. Whereas for comparison vitamin C has an IC 50 value of 15.448 ppm. From the results, it can be concluded that the ethanol extract of dengen bark has the ability to bind free radicals with IC 50 48.33 ppm