In hydrothermal carbonization, which is a kind of hydrothermal treatment process, biomass is treated in high temperature and high pressure water to produce solid product called hydrochar. The properties of the solid and liquid products change depending on the conditions including reaction temperature, time, and heating rate, which also affects the yield of hydrochar. However, the relationship between conditions and its effect differs from one researcher to another and has not been clarified. Therefore, we investigated the reaction characteristics of hydrothermal carbonization. We used glucose as the feedstock to investigate the behavior of char formation from water based solution. We considered a reaction model from previous studies and calculated the carbon yield of some substances using high performance liquid chromatography. The experimental values agreed with the calculated ones. The results of hydrothermal carbonization of glucose solution in a batch reactor are reported in terms of the product yields as a function of reaction temperature and time.