The effect of spilt-over hydrogen on catalysts which were prepared by physically mixing zeolites or alumina with SiO2-supported noble metals on chemisorbed pyridine was investigated by means of FTIR and TPD. It has been found that pyridine adsorbed on a Lewis acid site migrated to a Bronsted acid site under a hydrogen atmosphere. This suggests that spilt-over hydrogen should enhance the desorption of pyridine on the Lewis acid site, and that the possible state of spilt-over hydrogen on the Lewis acid site should be hydride, which has strong Lewis basicity. Furthermore, H-D exchange (-OH + D-2) of the Bronsted acid site was also carried out, which leads to a complete description of interactions between spilt-over hydrogen and acid sites of zeolite.