A new method to reduce methanol crossover in fuel cells is presented. This approach relies on coating an anode gas diffusion layer with poly(3,4-ethylenedioxythiophene), which is achieved by an electropolymerization method. Methanol permeability through commercially available gas diffusion layers was reduced from 4.5 × 10−5 to as low as 1.8 × 10−6 cm2 s−1. The use of the polymer increased the specific resistance from 0.07 to as high as 2.5 Ω cm2. Fuel cell testing demonstrated a positive shift in cell voltage of about 70 mV in the low current density region of the polarization curves.