Now a day, solid polymer electrolytes have attracted considerable attention owing to their reliable safety performance, electrochemical stability and exceptional flexibility, which make them superior to conventional liquid electrolytes. The prime requirements of solid polymer electrolytes are high ion conductivity. Since the conduction of ions occurs in the amorphous regions of the solid polymer electrolytes, it is really a matter of great interest to investigate the crystalline structure of solid polymer electrolytes prior to go any other characteristic. In this study, series of solid polymer electrolyte films based on polyvinyl alcohol (PVA) incorporated with the different concentration of magnesium chloride (MgCl2) were prepared using solution cast technique. X-ray diffraction (XRD) technique was used to characterize the crystalline structure of the prepared films. The XRD analysis of pure PVA film revealed that this polymer possesses a semi-crystalline structure. The XRD patterns of solid polymer electrolyte films proved that MgCl2 caused the decrease in the intensity of a characteristic peak of PVA at 2¿=19.55°, indicates the reduction in the semi-crystalline phase of the host.