A gel polymer electrolyte (GPE) film of poly(vinylidenefluoride) and magnesium triflate is prepared and studied for application in a solid-state rechargeable magnesium battery. The composition of GPE is optimized in view of minimum liquid components and maximum specific conductivity (σ). The σ of GPE of optimum composition is 2.67×10−3 Scm−1 at 20°C, and it follows a Vogel, Tamman and Fulcher equation with an activation energy of about 0.4kJmol−1. The effect of aging on the Mg/GPE interface is studied. The formation of a passivating film on the Mg surface, which increases in thickness on aging in GPE, is established. Several Mg/GPE/MnO2 cells are assembled and studied for discharge capacity and cyclic-life data. The results reveal that Mg/GPE/MnO2 cells at C/8, C/6 and C/4 discharge rates yield, respectively, capacities of 160, 80 and 50mAhg−1 of MnO2. These values are nearly constant for about 30 cycles. Further cycling of the cells leads to a decrease in capacity, which is attributed to passivation of the magnesium electrode and poor efficiency of the Mg2+ ion insertion into the MnO2 positive electrode.