The electrodeposition of polymethylthiophene films on mild steel from organic solution is reported. It is shown that homogeneous and very adherent polymethylthiophene films are formed after a special pretreatment with 2(3-thienyl)ethylphosphono acid. Polymethylthiophene films reduce the corrosion rate of mild steel but they cannot passivate the metal surface. A model is proposed which can explain the excellent adhesion properties of polymethylthiophene films, necessary for corrosion protection of mild steel.