AbstractThe term “hydrothermal” comes originally from the field of geology. Hydrothermal reactions generally can be defined as reactions in the presence of aqueous solvents under high temperature and pressure. Such reactions played a very important role during formation of fossil fuels. On the basis of the natural phenomena, we have conducted a series of studies concerning hydrothermal conversion of biomass into value-added products. This article gives an overview of some recent advances in our research on hydrothermal conversion of biomasses, mainly including the production of low molecular weight carboxylic acids, such as acetic acid, lactic acid, and formic acid, from carbohydrate and lignocellulosic biomasses, as well as glycerin, which is a by-product of the bio-diesel fuel manufacturing process.