In this work, we show the effect of the thermal treatment temperature on the photoelectrochemical (PEC) activity of CdSe/TiO 2 nanocomposites. TiO 2 nanotubes (NTs) were synthesized by anodization and the nanocomposites were obtained by depositing CdSe clusters via magnetron sputtering. A two-step thermal treatment was performed: heating the TiO 2 NTs at different temperatures prior to CdSe deposition and further heating the CdSe/TiO 2 nanocomposites. The nanocomposites were characterized by Rutherford backscattering spectroscopy (RBS), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), UV-Vis spectrophotometry, and electrochemical impedance spectroscopy (EIS). To compare the PEC performance of the CdSe/TiO 2 nanocomposites and pristine TiO 2 NTs, linear sweep voltammetry (LSV) curves were obtained under visible light and under 1 sun illumination. It was observed that CdSe incorporation into the TiO 2 template enhances the visible light absorbance thereby improving the PEC performance of the nanocomposites. We have found that the optical, structural and PEC properties of the CdSe/TiO 2 nanocomposites are dependent on the thermal treatment temperature of the TiO 2 nanotubular substrate, prior to CdSe deposition. Moreover, a three-fold improvement in photocurrent was observed upon further thermal treatment of the obtained nanocomposite. Effect of the thermal treatment temperature on the photoelectrochemical (PEC) activity of CdSe/TiO 2 nanocomposites.