The rearrangement of glucose to mannose was accomplished by ion exchanger resin supported molybdate catalysts in the liquid phase. Sodium molybdate and "molybdic acid" were used as catalyst precursor compounds. The fresh catalysts differ in their content of oligomer Mo species, as could be shown by UV-vis spectroscopy. The catalytic experiments were carried out in batch as well as in continuous mode. The highly selective rearrangement yielded up to 28.4% mannose in the batch and 27.2% in the continous reactor. A "molybdic acid"-based catalyst was tested during a long-term run over 800 h, however deactivation was observed to a certain extent as indicated by decreasing activity. The main cause for deactivation was Mo leaching. A method for the reactivation of used catalysts was elaborated. The initial activity could be received by reloading with fresh molybdate precursor and by reoxidation of reduced Mo species with 1% H2O2. (c) 2007 Elsevier B.V. All rights reserved.