Nickel oxide films were deposited by reactive d.c. magnetron sputtering. The microstructure and electrochromic properties of films deposited with different substrate temperatures were investigated. Transmission electron microscopy and X-ray diffraction studies on the microstructure have indicated that the sputtered nickel oxide films consist of cubic polycrystalline NiO. The NiO films deposited onto heated substrates have shown the texture of the (111) plane and a significant decrease in electrochromism. The causes which lead to the decline of electrochromic properties with the increasing of substrate temperatures have been interpreted as being associated with the microstructure.