Spectrophotometric quantification method of carbohydrates is useful for processing multiple samples. In this study, we established colorimetric quantification for 4- O -β-D-mannosyl-D-glucose (Man-Glc) and β-(1→4)-mannobiose (Man₂). For quantification of Man-Glc, phosphorolysis of Man-Glc catalyzed by 4- O -β-D-mannosyl-D-glucose phosphorylase (MGP) was coupled with quantification of D-glucose by the glucose oxidase-peroxidase method. In addition to MGP, cellobiose 2-epimerase (CE) was added for quantification of Man₂. In both quantifications, a good linear relationship was obtained between A ₅₀₅ and the sample concentration (0-0.5 mM). The A ₅₀₅ values obtained at various concentrations of Man₂ and Man-Glc were almost identical to those with equivalent D-glucose concentrations. Kinetic parameters of Ruminococcus albus and Rhodothermus marinus CEs for the epimerization of Man₂ were determined using the quantification method for Man-Glc. Both enzymes showed 5-15-fold higher k _cat/ K _m values than those for cellobiose and lactose, which supports the prediction that these enzymes utilize Man₂ as a substrate in the β-mannan metabolic pathway.