CuO/ZnO composites are synthesized using a simple mechanochemical combustion method. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier transform infrared (FTIR) are used to characterize the prepared oxides. X-ray diffraction reveals that the prepared CuO/ZnO exhibit a wurtzite ZnO crystal structure and the composites are composed of CuO and ZnO. The strong peaks of the Cu, Zn, and O elements are exhibited in the EDX spectrum. The FTIR spectra appear at around 3385 cm⁻¹ and 1637 cm⁻¹, caused by O–H stretching, and 400 cm⁻¹ to 590 cm⁻¹, ascribable to Zn–O stretching. The photocatalytic performances of CuO/ZnO nanocomposites are investigated for the degradation of methylene blue (MB) aqueous solution in direct solar irradiation. The degradation value of MB with 5 wt % CuO/ZnO is measured to be 98%, after 2 h of solar irradiation. The reactive ^•O₂⁻ and ^•OH radicals play important roles in the photodegradation of MB. Mineralization of MB is around 91% under sunlight irradiation within 7 h. The photodegradation treatment for the textile wastewater using sunlight is an easy technique—simply handled, and economical. Therefore, the solar photodegradation technique may be a very effective method for the treatment of wastewater instead of photodegradation with the artificial and expensive Hg-Xe lamp.