The redox reactions of methylene blue (MB) incorporated into polypyrrole (PPy) on pyrolytic graphite (BPG) electrodes were investigated by the potential-modulated electroreflectance (ER) method. The incorporation of MB into the PPy film was achieved by either electropolymerization of pyrrole in the presence of MB or polarization of the PPy-coated electrode at negative potentials in an MB solution. The ER spectrum of MB incorporated into the PPy-film, which was similar to that of MB adsorbed directly to the BPG electrode, suggested that MB in the PPy film diffused out during deaeration of the electrolyte solution and only MB adsorbed on the BPG electrode surface reacted. In the presence of MB in both the PPy film and solution phase, the measured ER spectrum was the sum of the ER spectra of MB adsorbed on the BPG electrode surface and MB in both the PPy film and solution phase. Each of the two spectra was detected separately using the phase-shift method.