Nickel oxide thin films were deposited by chemical spray pyrolysis. The influence of the nickel sulfate hexahydrate (NiSO4 center dot 6H(2)O) precursor on the thin film properties was studied. Present experimental conditions such as the substrate temperature and precursor concentration which are 350 degrees C and 0.3 M, respectively, were investigated. It is found that pure NiO thin films crystallized in the cubic phase. Nickel oxide thin films have been annealed at 42.5 degrees C for 3 h under vacuum. It is found that annealing under vacuum is more efficient for the NiO films under the present experimental conditions. After the annealing process NiO thin film was evaluated by XRD, SEM and optical microscopy.