Thin films of Cu2ZnSnS4 (CZTS), a potential candidate for absorber layer in thin film heterojunction solar cell, have been deposited by spray pyrolysis technique onto soda-lime glass substrates held at a substrate temperature (Ts) of 643 K. The effect of copper salt and thiourea concentrations on the formation of Cu2ZnSnS4 thin films is investigated. CZTS films formed under optimized conditions are found to be polycrystalline in nature with kesterite structure. The lattice parameters are found to be a = 0.543 nm and c = 1.086 nm. The optical band gap of these films is found to be 1.43 eV. It is found to increase with decrease in copper salt concentration in the solution.