In this study, Ziziphus nummularia leaves extract was applied for the synthesis of CuO nanostructures. The material was characterized by various techniques such as Infrared (IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray (EDX) and scanning electron microscope (SEM) analysis. The characteristic peaks in powder XRD pattern of nanostructured of CuO at 2θ of 32.33, 35.57, 38.71, 46.11, 48.80, 51.50, 58.22, 61.58, and 68.08◦, correspond to (110), (-111), (111), (-112), (-202), (112), (202), (-113), and (220), respectively, match with diffraction patter of standard monoclinic phase of CuO (JCPDS: 01-080-1916). Tauc plot was plotted and band gap energy was calculated, and found to be 2.4eV. The material was tested as photocatalyst for degradation of MB, and worked well at optimum parameters such as dosage of catalyst 25mg, concentration of MB 20.0mgL-1, pH 7 and time 120min. The proposed method worked very well on synthetic solutions with degradation efficiency (%) ≥83.51 and an RSD (%) of ≤4.0.