Glucose decomposition kinetics was studied under supercritical pressure of 25 MPa in the temperature ranging from 448 to 673 K using a continuous reactor. It is usual that the reaction is assumed to be of the first order to determine the reaction rate coefficient, but in this Study, reaction order was also determined from the experimental data, and reaction order less than unity was observed at a high temperature. Considering that reaction field changes from ionic to radicalic as temperature increases front 448 to 673 K, change in reaction mechanism is implied.