Hydrothermal process is a thermochemical process used to convert wet biomass waste become a coal-like material with higher carbon content called hydrochar. In this study, performance test of hydrothermal reactor was done. Stirred reactor was made of SS-304 with volume of 1 L and electric heater as a heating mantle. The hydrothermal carbonisation reactor was utilized to perform the carbonisation of three materials (paper, banana peel, and sawdust) as substrates. The substrates represent major component of biomass waste in Bandung, Indonesia. Process was operated in batch-mode at varying temperatures (190 °C, 210 °C and 230 °C), holding time (30 and 60 min), and solid load (1:3, 1:5, and 1:10). The results suggested that the hydrothermal conversion of biomass waste to solid fuel gave high heating value with value of 24.6, 21.2, and 20.1 MJ/kg for sawdust, paper, and banana peel respectively after product dried naturally. The study showed that chemical and physical properties of several feedstock and hydrochar varied as a function of reaction temperature.