In this study, the waste leaves of Euryale ferox Salisb. as a potential source of anthocyanins was investigated. Ultrasound-assisted technique with Box–Behnken design was applied for optimization of the anthocyanins extraction from Euryale ferox leaves. As a result, the optimal extraction condition was as follows: ultrasound temperature was 40 °C, ultrasound time was 38 min, ethanol concentration was 62% (v/v) and solvent-to-solid ratio was 27 mL/g. And the maximum yield of anthocyanins was 281.56 ± 3.02 mg/100 g under the optimum extraction parameters. The experimental data was close to the predicted anthocyanins yields of 289.45 mg/100 g and significantly higher than the yield of 181.81 ± 1.94 mg/100 g obtained by conventional solvent extraction. Moreover, the result of HPLC-QTOF-MS/MS analysis identified nineteen compounds in the purified anthocyanins extracts. And the anthocyanins extracts exhibited high scavenging activities on α,α-diphenyl-β-picrylhydrazyl and 2,2′-azinobis- (3-ethylbenzthiazoline-6-sulphonic acid) radicals. Results implied that Ultrasound-assisted extraction was a suitable method for anthocyanins extraction from Euryale ferox leaves with good antioxidant activities, and Euryale ferox leaves could be a potential source of natural anthocyanins used as antioxidant in functional food or medicine.