This paper reports the effect of pH on chemical bath deposited polyaniline (PANI) thin film properties. Various analytical techniques have been used to study morphological, structural and optical properties. The smooth surface morphology observed in PANI film prepared at lower pH has become rough with increase in pH value. In UV-vis spectra, two peaks are observed at 400 nm and 800 nm and the peak observed at 800 nm is shifted toward higher wavelength with increase in pH value. The Cl is introduced in the B ring of the PANI that makes PANI more oxidized with decrease in pH value. In XPS N-1s core level spectra also, PANI is observed in more oxidized state with decrease in pH value. This indicates that the pH of monomer solution varies the morphology, structure, oxidation state as well as the conductivity of the film. (C) 2014 Elsevier B.V. All rights reserved.