In this study, the effects of concentration of cellulase preparation and hydrolytic time on the level of total phenolics, anthocyanins, vitamin C and the antioxidant activity of the mulberry juice were investigated. Response surface methodology was then used to optimize the treatment conditions for maximizing the phenolic level in the obtained juice. The optimal concentration of cellulase preparation and hydrolytic time were 0.17 percent w/wand 106 min, respectively. Under these conditions, the maximal phenolic content in the extract achieved 1676 mg gallic acid equivalent per liter and the antioxidant activity was 14.71 millimole trolox equivalent (FRAP method) and 13.02 millimole trolox equivalent per liter.