Supercritical water gasification is suitable for wet biomass gasification. It is thought that dry matter content of feedstock has some effects on its reactivity, while the effects and mechanism are still unclear. In this study, we focused on dry matter content of feedstock and its effect on reactivity and decomposition products. We employed glucose solution as a model feedstock of biomass. The experimental setup was customized to realize rapid heating up and cooling down, which minimized the effect of heating up and cooling down process. It was founded that the reaction rate became lower when the glucose concentration became higher. And its effect became small when the reaction temperature was lower than 523 K.