Abstract: Hydroxy-functionalized 3,4-ethylenedioxythiophene(EDOT-OH) is an important derivative of 3,4-ethylenedioxythiophene(EDOT). EDOT-OH was chemically vapor deposited on the spin-coated FeCl₃ oxidant films from FeCl₃/butanol solutions with different concentrations to prepare a series of PEDOT-OH films. The structures and morphologies of PEDOT-OH films were characterized by micro-infrared, Raman spectroscopy and field emission scanning electron microscopy and the effect of FeCl₃/butanol solution concentration on the thicknesses of spin-coated FeCl₃ oxidant film and PEDOT-OH film were investigated. EDOT-OH was deposited on a gold finger electrode to prepare an organophosphorus poison sensor and its performance was evaluated. The results revealed that the thickness and the doping degree of PEDOT-OH film increased with the in crease of concentration of FeCl₃. The results suggested that the prepared sensor had good responsiveness, sensitivity and repeatability.