Nickel oxide films have been deposited from nickel chloride solution by spray pyrolysis technique onto glass substrates at different substrate temperatures "T-sub ". X-ray diffraction (XRD) analysis showed that, at low T-sub, amorphous films have been obtained, while at higher T-sub > 275degreesC, crystalline NiO with preferential growth along (1 1 1) plane. From measurements of spectral transmittance and reflectance, and on the basis of Murmann's exact equations, the optical constants have been computed over the spectral range 300-2500nm. Analysis of the spectral absorption confirmed direct and indirect transitions with values markedly affected by Tub due to structure and off-stoichiometry changes of the formed films. The dark electrical resistivity drops with three orders of magnitude for films deposited at higher substrate temperature due to improvement in crystallinity. The results have been interpreted by assuming two-phase model. Infrared spectral reflectance showed presence of nickel chloride in films formed at T-sub less than or equal to 225degreesC, which is consistence with XRD findings and claiming incomplete pyrolytic reaction. (C) 2003 Elsevier B.V. All rights reserved.