Optimization of antioxidant capacity from Persicaria barbata leaf extract was conducted using response surface methodology (RSM). The conditions investigated were 90 – 150 min extraction time (x1), 60 – 75%v/v ethanol concentration (x2) and 30 – 50 v/w liquid-to-solid ratio (x3) while a fixed extraction temperature at 95 ?C was chosen. The quality of fit to the second-order polynomial models was confirmed based on the coefficient of determination of 0.9581. Box-Behnken experimental design indicated that models can significantly (p< 0.05) express more than 80% ( > 0.80) of the response variation. The order of factors influencing the response value of antioxidant capacity was ethanol concentration, extraction time and liquid-to-solid ratio, respectively. The optimal extract condition for maximum antioxidant capacity was 120 min of extraction time, 60% (v/v) of ethanol concentration, 40: 1 mL/g of liquid-to-solid ratio and extraction temperature at 95 ?C. The ascorbic acid equivalent antioxidant capacity (AEAC) value obtained from experiment was 93.825 ? 0.15 mg AEAC/ g of dried plant.