In this study, ultrasound pretreatments of sunflower-meal protein (SMP) to yield high antioxidant capacity from its hydrolysates by response surface methodology were optimized. Optimization of experimental conditions was achieved to examine the impact of temperature, solvent-solid ratio and sonication time on antioxidant capacities of SMP hydrolysates with Box–Behnken's design. Quadratic models of DPPH-scavenging activity (DPPHSA), hydroxyl-radical scavenging activity (HRSA), and Cu2+ and Fe2+ chelating activity (Cu2+-CA and Fe2+-CA) were developed, and their coefficients observed from multiple-regression analysis. ANOVA indicated that time was highly significant (p < .01) on all experimental responses. The best experimental point of DPPHSA, HRSA, Cu2+-CA, and Fe2+-CA was accessed at 42.50
C, 18.16 mL/g and 26.52 min and the predicted data for these responses were 52.09, 70.05, 50.85, and 43.35%, respectively. Outcome of verification experiment was reliable with predicted data for all responses. Additionally, DPPHSA, HRSA, Cu2+-CA, and Fe2+-CA of pretreated hydrolysate improved (p < .05) by 17.41, 20.00, 14.72, and 26.41%, respectively over nonsonicated hydrolysate. Amino acid content and hydrophobicity of SMP hydrolysate at the optimum sonication condition were analyzed. Analyses indicated that ultrasonication could facilitate the releasing/unfolding of hydrophobic amino acids from SMP over nonsonicated samples during enzymolysis with high antioxidative capacity.