A simple and inexpensive spray pyrolysis technique (SPT) was employed to deposit nickel oxide (NiO) thin films from hydrated nickel chloride salt solution on to glass substrates. The thermogravimetric analysis (TGA) and differential thermal analysis (DTA) techniques were used to study the thermal characteristics of the precursor salt. The effect of the volume of sprayed solution on structural, optical and electrical properties was studied using X-ray diffraction (XRD), infrared (IR), optical absorption, electrical resistivity and thermoelectric power (TEP) techniques. It is found that increase in the volume of sprayed solution leads to the increment in film thickness and amelioration of crystallinity of the film, consequently the band-gap energy wanes from 3.58 to 3.4 eV. It also affects resistivity and TEP of the film. (C) 2002 Elsevier Science B.V. All rights reserved.