Nafion membranes were prepared by incorporating in the polymer matrix the 1-butyl-3-methylimidazolium (BMI+) ionic liquid cation at different doping levels. Increasing the doping time of the membranes with the ionic liquid results in increased incorporation of the BMI+ cation but a decrease in the bulk conductivity. The thermogravimetric analysis shows that the BMI+ cation incorporation increases the thermal stability of the membranes. The higher discharge efficiency of the fuel cell at 80 degrees C was obtained by using Nafion membrane after 15minutes of doping in the ionic liquid solution.