Proton exchange membranes have been synthesized from polyimide (PI) doped with different contents of montmorillonite (MMT) which was obtained by solution casting technique. The enhancement of conductivity was achieved through modification with the MMT. Prepared membranes were systematically characterized in terms of ion exchange capacity, water uptake, methanol uptake, swelling behavior and proton conductivity. Fourier transform infrared spectroscopy and X-ray diffraction measurements were used to confirm the structures of the PI/MMT composite electrolyte membranes. SEM surface morphological images of the composite membranes showed that the MMT nanoclay particles were dispersed uniformly within the membrane what was also reflected in XRD results which indicated a good compatibility of MMT particles with the polymer complex. The TGA spectra showed that the thermal stability of the membrane was reduced by adding MMT into the polymer network. The prepared membrane with 10 wt.% of modified MMT exhibited the highest proton conductivity value of 7.06 × 10-2 S·cm-1 at 70 °C. These results imply the potential application of the PI/MMT composite membranes as improved PEMs for DMFC applications.