Abstract: The ethanol extracts from the roots of Mokara (ERM) were extracted with ultrasonic and analyzed for its antioxidant activity and stability. The antioxidant activity of ERM was measured the capabilities for scavenging hydroxyl radical and DPPH radical. The effects of pH, temperature and light on the stability of ERM were investigated. The results showed that the optimal technological conditions:anhydrous ethanol, m (roots of Mokara, mg) ∶ v (EtOH, mL) =25∶25, 50℃, 60min, 48W. Under the optimized conditions, the antioxidant activity of ERM was better and the scavenging rate of DPPH radical reached 92%. The median inhibitory concentration (IC50) of scavenging hydroxyl radical and DPPH radical were 34.62μg/mL and 45.20μg/mL, respectively. The roots of Mokara were natural antioxidants, which had strong antioxidant activity and better stability.