Response surface methodology was used to optimize experimental conditions for ultrasonic-assisted extraction of phenolic compounds from blackberry leaves. The Box-Behnken design (BBD) was employed for the optimization of extraction parameters in terms of total phenolics and antioxidant capacity. The optimal conditions for results of ABTS and CUPRAC were HCI concentration 0.41 and 0.45 M, methanol concentration 61 and 64% (v/v), extraction temperature 66 and 68 degrees C and extraction time 105 and 117 min, respectively. The experimental values agreed with those predicted values within a 95% confidence level, thus indicating the suitability of response surface methodology in optimizing the ultrasound-assisted extraction of phenolic compounds from blackberry leaves. The results showed that phenolic compounds present in blackberry leaves exhibited significant antioxidant properties. Seven phenolic compounds such as ellagic acid, caffeic acid, chlorogenic acid, quercetin, myricetin, kaempferol and kaempferol 3-beta-D-glucopyranoside were determined in blackberry leaves by HPLC-DAD after extraction at optimum conditions. (C) 2012 Elsevier B.V. All rights reserved.