Decomposition of disaccharides consisting of two glucose residues or glucose and fructose or galactose residues was measured using a tubular reactor at various residence time under the condition of 160 to 260°C and 10 MPa. The decomposition processes were expressed by the Weibull equation for all the disaccharides at any temperature. The susceptibility to decomposition depended on the type of glucosidic bond and was related to an electrostatic potential charge on the oxygen atom in the bond. Detail studies for decomposition kinetics were performed for maltose and sucrose. A change of pH during the decomposition intensively affected the decomposition rate, which could be also expressed by autocatalytic equation for sucrose decomposition.