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