The ultrasound-assisted extraction of Juglans nigra L. leaves was optimized with respect to total phenolic content (TP) of the extracts by varying the concentration of aqueous ethanol solution (E) and different solvent-to-solid ratio (S). The influence and optimum of the operating parameters (E and S) was examined using response surface methodology (RSM). The statistical criteria indicated the adequacy, reliability and precision of the developed RSM model. RSM showed that maximum extraction yield of TP 28.59 mg g -1 of draw plant was achieved at the optimal values of 50% E and 20 kg kg -1 S. Using the modelled optimized conditions, the detected relative difference between the predicted and the experimental yield was ±2.3 %. The determined TP content in the extracts varied from 12.54 to 29.26 mg GAE g -1 of dry plant indicated that J. nigra is a valuable source of phenolic substances. The extracts of J. nigra leaves obtained under optimal conditions showed good antioxidant activity (IC 50 = = 18.91±0.03 μg cm -3 ) which was determined by the scavenging effect on 2,2--diphenyl-1-picrylhydrazyl radical. The optimization of the TP extraction process is the important step in improving techno-economics of the potential commercial preparation of J. nigra extracts, as natural source of antioxidants.(CC) 2018 SCS.1274 GAVRILOVIĆ et al. ivity of black walnut, as well as ability of black walnut to depress the tumour growth rate and to prevent lead induced testicular toxicity in rats. [2][3][4][5] The polyphenolic compounds, important parameters in assessing the quality of numerous natural products, are responsible for beneficial health effect these products exhibit. 6 The polyphenolic profiles of bark, sapwood and heartwood, leaves and husks from J. nigra were characterized using different polyphenols (juglone, α-hydrojuglone-4-glucoside, myricetin, myricitrin, sakuranetin, sakuranin, neosakuranin and o-diphenols). [7][8][9] The extraction of polyphenolic compounds from Juglans species has been carried out with methanol and ethanol as solvents. [10][11][12] In recent years two extraction methods such as ultrasound-assisted (US-AE) and microwave-assisted extractions have been used for the extraction of polyphenolic compounds from the leaves of Juglans species. 11,12 US-AE offers a series of advantages such as improved efficiency, reduced extraction time and temperature. 13,14 There several reports on the ultrasound-assisted extraction of polyphenols from J. regia leaves. 11,15 On the other hand, there is no data on US--AE of total phenolics (TP) from J.nigra leaves.Many factors, such as solvent concentration, temperature and extraction time, have been determined to influence the US-AE efficacy of polyphenolic compounds from J. regia leaves. 11 Optimization of ultrasound extraction and simultaneous microwave/ultrasonic-assisted extraction of phenolic compounds from J. regia was assessed. 11,16 Despite the interesting properties of J. nigra and its extracts, there is lack of data regarding the optimal conditions for the pol...