Composite photocatalysts composed of NiO and CaO have been prepared via mechanically mixing of the two powders. The as-synthesized NiO-CaO products were characterized by X-ray diffraction (XRD) and UV-vis spectrometry. The experimental results showed that the absorption wavelength range of the mixed NiO-CaO sample was notably extended towards the visible-light region (400-450 nm). Photocatalytic activity of the NiO-CaO composite was evaluated based on the decomposition of methylene blue under visible-light irradiation. The effects of CaO doping and the duration of heat treatment on the durability of the NiO-CaO products have been investigated in detail. Factors influencing photocatalytic activity and the mechanism of photocatalysis were also addressed. Published by Elsevier B.V.