In this work, copper sulphide (CuS) thin films were deposited on glass substrates by chemical bath deposition method under different pH, deposition temperature, stirring speed and deposition time. The effects of process parameters, such as pH from 1.8 to 2.2, deposition temperature from 30 to 50 degrees C, stirring speed from 50 to 250 rpm and deposition time from 8 to 40 h on the band gap, were optimized by central composite design (CCD) of response surface methodology (RSM). Five-level-four-factor CCD was employed to evaluate the effects of the deposition parameters on the band gap of CuS thin films. A quadratic model was established as a functional relationship between four independent variables and the band gap. Analysis of variance revealed that the proposed model was adequate. The optimum pH, deposition temperature, stirring speed and deposition time were found to be 2.10, 44.33 degrees C, 200 rpm, and 32h, respectively. Under these conditions, the experimental band gap of CuS was observed as 2.74 eV, which was well in close agreement with predicted value (2.71 eV) by the model. (C) 2015 Elsevier B.V. All rights reserved.