A gel polymer electrolyte (GPE) film of poly(methylmethacrylate) and magnesium triflate is studied in view of its potential application in a solid state rechargeable magnesium battery. Experimental data of a.c. impedance and cyclic voltammetric studies of symmetrical cells made of blocking and non-blocking electrodes, and also data of charge/discharge cycles of Mg/GPE/MnO2 cells are reported. The composition of the GPE is optimized in view of a minimum quantity of the liquid components (propylene carbonate and ethylene carbonate) required for the gel formation and a maximum conductivity. Specific conductivity (σ) of the GPE of optimum composition is (4.2±0.45)×10−4 S cm−1 at 20°C. The σ values follow the Arrhenius equation and the activation energy for GPE of optimum composition is 0.038 eV. The effects of temperature and ageing on Mg/GPE interface are studied. Discharge capacity of about 90 mAh g−1 of MnO2 is obtained during the discharge of Mg/GPE/MnO2 cells. On repeated charge/discharge cycling of the cell, the discharge capacity decreases to about 70 mAh g−1. The cycle-life is limited by the problems associated with passivation of the Mg surface.