Zinc oxide thin films were deposited by successive ionic adsorption and reaction (SILAR) method using a zinc sulphate and sodium bath on glass substrate. The effect of pH, though one of the important factors, which determine the quality of films, is usually ignored. The present work explores the effect of pH of solution on the structural, morphological and optical properties of thin films. X-ray diffractograms and scanning electron microscopy reveal that the grain size is increased with the increase in pH of the precursor solution. The optical studies show that the band gap decreases from 3.29 to 3.09 eV with increase in pH.