A kinetic analysis is presented for the homogeneous degradation of galactoglucomannan (GGM) in hot water extraction conditions. In the experiments used for constructing the kinetic model, GGM extracted from spruce wood meal was treated at temperatures from 150 to 170 degrees C and in buffered pH 3.8-4.2. The hydrolysis of glycosidic bonds in GGM was modeled as a random process which is catalyzed by hydrogen ions. The real hydrogen ion concentration at the reaction temperatures was estimated. The Arrhenius equation was used to describe the temperature dependence of the hydrolysis rate and an activation energy of 102 kJ/mol was obtained for the reaction. The presented model predicts accurately the evolution of the molecular weight distribution with lower computational load than other similar models.