The preparation and properties of poly(acrylic acid) (PAA)-doped polyaniline (PANI) film electrodes further modified by electrodeposition of platinum particles were investigated by cyclic voltammetry and in situ conductivity measurement. The PANI/PAA film exhibits a better electroactivity and higher stability, even in solutions of lower acidity, although its polymerization rate is decreased threefold compared to that of PANI. The conductivity of the PANI/PAA film increases by a factor of two compared to that of PANI. The effects of the carboxylic acid groups of PAA in the PANI matrix on the performance of the film are discussed. The electrocatalytic activity of PANI/PAA/Pt for reduction of hydrogen and oxidation of MeOH is higher than that of PANI modified with Pt particles alone. Characterization of the electrodes by SEM shows the platinum modification procedure yields roughly spherical catalyst particles 0.5-1 mu m in diameter dispersed throughout the polyaniline.