Modulated zirconium metal‐organic framework UiO‐66 is shown to catalyze the isomerization of D‐glucose to D‐fructose in alcohol media. Fructose selectivity can change depending on solvent choice. We hypothesize that the difference in selectivity is due to a combined effect of adsorption and solvation effects, which may lead to the high formation of alkyl‐glucosides in depletion of fructose when methanol or ethanol are used. A fructose selectivity of 72 % at 82 % glucose conversion in 1PrOH was achieved. The reaction mechanism was investigated using nuclear magnetic resonance spectroscopy. We demonstrate that UiO‐66 isomerizes glucose to fructose via intramolecular C2‐C1 hydride transfer. In addition, we show that modulated UiO‐66 is a highly active and stable catalyst at the reaction conditions, showing great potential for other sugar reactions.