Abstract: A cellulose-containing biomass such as wood is liquefied by heat-treatment under a pressurized condition in the presence of water and a neutral, oxygen-containing organic liquid such as an ester, ether, ketone or alcohol. An alkaline catalyst such as potassium carbonate may be added to accelerate the liquefaction when the organic liquid is one other than acetone. Also provided is a process for the liquefaction of a cellulose-containing biomass including heat-treating the biomass in an aqueous medium in the pressurized atmosphere of an inert gas or steam at a temperature of 250.degree.-385.degree. C. in the presence of an alkaline catalyst in an amount of 0.01-0.1 part by weight per one part by weight of the biomass on the dry basis.