Cu2ZnSnS4 thin films with different tin concentration are deposited over ITO coated glass substrates using chemical spray pyrolysis technique, by adjusting [Sn]/[Zn] ratio as 0.7, 1 and 1.3 in the precursor solution. As prepared films are subjected to sulfurization at a temperature of 500 degrees C for 15 min and its effect on the structure and composition of the films is studied. Sulfurization is carried out under non-vacuum condition inside the spray pyrolysis chamber making it compatible with the deposition technique. Pristine and sulfurized films are analysed using X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy, UV-Vis-NIR spectroscopy and scanning electron microscopy. X-ray diffraction and Raman spectroscopy suggest the formation of Cu2ZnSnS4 and other binary compounds in the pristine films. Analysis of the sulfurized films indicates that the sulfurization process has brought about a significant change in the composition of the films while improving its crystallinity considerably. Compositional analysis using X-ray photoelectron spectroscopy reveals that substantial amount of indium from the underlying ITO has diffused into the film after sulfurization. However, it is observed that increase in concentration of tin in the film limits the diffusion of indium. Scanning electron microscopic images show the improvement in morphology of the films after sulfurization.