Zinc iodide (ZnI2) crystalline thin film is produced with chemical bath deposition on substrates (commercial glass). The pH of chemical bath is scanned with controlled potassium hydroxide. Some properties of films changed with pH and changes of pH were analyzed. The pH values are scanned at 6.01-6.29. Transmittance, absorption, optical band gap and refractive index are investigated by UV/Vis. spectrum. The hexagonal and tetragonal form in structural properties in XRD at pH: 6.01 were seen. The pH of bath was up to 6.01, KZnI3 center dot 2H(2)O (orthorhombic), KZnI3 center dot(H2O)(2) (orthorhombic), ZnI2 (tetragonal) and ZnI2 (hexagonal) forms were observed in XRD patterns. The structural and optical properties of ZnI2 thin films analyzed at different pH. SEM analysis studied for surface analysis in films. The SEM analyses were agreed with XRD patterns. The optical band gap increased with pH between 3.4 and 3.6 eV. The film thickness changed with pH at 108-345 nm. Also refractive index and transmission generally increased with pH. (C) 2015 Published by Elsevier B.V.