TiO₂/ZnO nanocomposites with ratio of Ti/Zn of 1:0, 1:1, 2:1, 3:1 and 0:1 was synthesized by sol–gel and hydrothermal methods. The performance and the photocatalytic of the nanocomposities mechanism were studied by X-ray diffractometer (XRD), Fourier transformed infrared (FT-IR), Brunauer–Emmett–Teller method (BET), Transmission Electron Microscopy (TEM), High-Resolution Transmission Electron Microscope (HRTEM) and UV–visible diffuse reflectance spectra (UV-Vis), respectively. The results showed that TiO₂/ZnO nanocomposites successfully prepared at different Ti/Zn rations. HRTEM results clearly heterojunction structure, and it can reduce the band gap width of the composite and improve the optical absorption intensity. Besides, the degradation rate of methylene blue (MB) of TiO₂/ZnO nanocomposites with a Ti/Zn ratio of 2:1 was close to 100% at 80 min, which was better than the other four samples. The photocatalytic degradation reaction confirmed to the first-order kinetic equation. The kinetic constant of TiO₂/ZnO nanocomposites with a ratio of 2:1 is 0.03748 min⁻¹, which is 2.8 times of pure ZnO and 4.8 times of pure TiO₂, respectively. In addition, the major active species of the photocatalytic reaction are •OH and h⁺ through activity capture experiments. The improvement of the catalytic performance of TiO₂/ZnO nanocomposites is mainly due to the ability to separate holes and electrons.