In this paper, we report the synthesis and properties of a series of composite polymer electrolytes formed by dispersion of a non-ionic organic plastic material succinonitrile (SN) into poly (vinyl alcohol) complexed with magnesium acid salt. Scanning electron microscope (SEM) images of different SN concentrations of films revealed that large open pore structure were also frequently present, when SN content increase up to 7.5 wt %. The addition of SN greatly enhances ionic conductivities of the electrolytes which is due to the high polarity and diffusivity of SN. The Mg2+ ion conduction is confirmed from impedance spectroscopy and transport number measurements. The highest conducting sample in the plasticized system was used to fabricate magnesium battery with configuration Mg/SPE/TiO2. The discharge capacity of the fabricated battery was 17.5 mAh/gm.