The epimerization of carbohydrates with molybdate catalysts has been investigated using a microstructured reactor. Parametric screening tests were performed with different catalyst concentrations ranging from 0.02 wt.% to 0.2 wt.%, with and without H2SO4, in the temperature range from 130 degrees C to 200 degrees C and at different total flow rates from 1 ml/min to 10 ml/min. The results achieved by this current work show that the addition of H2SO4 for the reaction is not necessary. The molybdate-catalyzed conversion in a microreactor in continuous flow regime provides especially high yield of mannose to approx. 30-32% at T-Reaction = 160-200 degrees C with catalyst concentration of 0.2 wt.%. The tested reaction in a microstructured reactor needs a smaller flow rate in the area between 1 ml/min and 2 ml/min, which results in a longer residence time. No by-product like hydroxymethylfurfural (HMF) was observed with the tested catalyst concentration of 0.1 wt.%. The ratio of glucose to mannose changes from 3:1 to the range (1.7-2):1. The continuous flow operation in a microstructured reactor exceeds the previously known yield of mannose with a ratio 3:1 found in actual literature data. (C) 2016 Elsevier B.V. All rights reserved.