The site conversion of some bridged (b-) methoxy species to the terminal ones on ZrO2 was directly observed by infrared spectroscopy between 523 and 623 K, accompanied by thermal decomposition of coadsorbed formate species. The observed site conversion was interpreted in terms of methoxy migration on the ZrO2 surface, which was previously supposed to occur in the H/D isotope exchange reaction of both methoxy groups with b-OD groups.