In this study, the effect of process variables, such as temperature, biomass: water ratio and reaction time, in hydrothermal carbonization (HTC) has been studied for different type biomasses. Response surface methodology was used to study the influence of each factors as well as their combined interactive effect on the mass yield and energy density of hydrochars. The results showed that the temperature and time were significant factors effecting the mass yield and energy densification ratio in HTC of the sunflower stalk and algae, whereas temperature was only significant factor in HTC of poultry litter. The biomass: water ratio was found insignificant for all tested biomasses. In addition, the fuel properties of hydrochars were compared with the properties of biochar derived from torrefaction at 300 degrees C. The results showed that for all tested biomass, the biochars had lower volatile matter and fixed carbon than hydrochars.