Undoped and Mn-doped zinc sulfide thin films were prepared on glass substrate by spray pyrolysis technique (SPT). XRD, AFM and UV–visible spectra measurements were done to explore the effect of doping on structural and optical properties of ZnS films. X-ray diffraction illustrates polycrystalline nature of the films increases via increasing Mn doping. Crystallite size evaluated by Scherrer’s formula shows increasing with increasing doping. Average diameter for undoped ZnS is 84·78 nm and it increases to 96·93 nm for 3%Mn-doped ZnS. As Mn doping concentration increases optical band gap of films decreases.