Polypyrrole-tetrathiomolybdate-molybdenum trisulfide, PPy-MoS42--MoS3, thin film coated tin oxide electrodes have been studied by W-visible spectroscopy. The films are obtained by electrochemical polymerization from an aqueous solution of 0.5M pyrrole and 0.5 mM (NH4)(2)MoS4 at a potential of 0.7 V vs. SCE. The UV-visible spectroscopy data suggest that both tetrathiomolybdate anions and molybdenum trisulfide are released from the film during the initial reduction sweep. potential cycling also induces a modification of the polymer structure involving loss of long-range order which is evidenced by a decrease of absorbance. Analysis of the absorbance data at 380 and 720 nm according to Nernst law enabled the determination of the redox potentials which were found to be equal to -0.26 and 0.07 V,respectively. The former is related to polaron generation in the bandgap while the latter can be attributed to bipolaron production in the bandgap.