Poly(3,4-ethylenedioxythiophene) (PEDOT) was electropolymerised on aluminium substrates. The Al/Al oxide/PEDOT junction was studied by electrochemical impedance spectroscopy, comparing the impedance response of the polymer film in oxidised, neutral and reduced form. The p- and n-doping behaviour of the PEDOT films was studied by in situ external reflection Fourier transform infrared spectroscopy during stepwise potential cycling of the films. The Al surface underneath the polymer was analysed with X-ray photoelectron spectroscopy. The impedance spectra indicate that an insulating layer between the metal and the polymer grows thicker during doping of the polymer film. The other techniques used suggest that this interfacial layer consists mainly of Al oxides and fluorides. Neither the conductivity nor the dopability of the polymer is notably affected by the growing of this insulating interfacial layer, which makes the concept of PEDOT electropolymerised on Al promising from an organic electronics applications point of view.