ZnS thin films were grown on soda lime glass substrates using spray pyrolisis method at a substrate temperature of 573K. The films were then subjected to a rapid thermal annealing at different temperatures. X-ray diffraction carried out on the films revealed a single peak which increase in intensity with increase in annealing temperature. The patterns of the ZnS thin films showed that the full width at half-maximum (FWHM), micro-strain and dislocation density of the films decreased with increase in annealing temperature, indicative of an improvement of the crystal quality of ZnS films. Similarly the calculated grain size of the films exhibited an increase with increase in annealing temperature which is a clear indication of an improvement of the crystal quality of the ZnS films. The values of lattice constant 'a' agree with the standard and reported values.