Single-phase Cu2ZnSnS4 (CZTS) thin films have been spray deposited on glass substrate, using uniform size oleic acid coated CZTS nanoparticles and the effect of heating temperature (75 degrees C to 300 degrees C) on the structural and optical properties have been investigated. X-ray diffraction results confirmed the formation of the single phase CZTS with a preferred orientation in (112) plane. The crystallite sizes of these films are similar to 7.0 +/- 0.5 nm but the intrinsic strain present in the nanostructured films decreases from 9.1 x 10(-3) to 1.3 x 10(-3) with the increase of the heating temperature from room temperature to 300 degrees C. Optical band gap of the as deposited CZTS films is similar to 1.72 eV and it decreases to 1.45 eV for the CZTS films heated at 300 degrees C. The observed red shift in the band gap of CZTS films with the heating temperature has been attributed to a reduction in the intrinsic strain present in the film with the increase in the heating temperature.