The adsorption of CO on polycrystalline TiO2 was investigated by static adsorption microcalorimetry. The initialdifferential heat of adsorption (qdiff,0) of CO on polycrystalline titania is 40 kJ/mol, and the standard adsorption entropy(Δs0) is −104 J mol-1 K-1. These results are consistent with those derived from temperature-programmed desorptionand FTIR results in the literature. The good reproducibility of the isotherms and the stable qdiff indicate that the latticeoxygen and hydroxyl groups on titania surface are basically not reactive to adsorbed CO.