Abstract: A process for pretreating a lignocellulosic plant raw material in order to obtain a pretreated material that is capable of being hydrolyzed and fermented for the production of bioethanol, includes the following successive steps: (i) destructuring the lignocellulosic plant raw material by placing it in the presence of a mixture containing formic acid and water, at a reaction temperature between 95° C. and 110° C.; (ii) then, at atmospheric pressure and prior to any hydrolysis then fermentation action, separating: on the one hand, the solid phase, mainly composed of the cellulose, constituting a first co-substrate, capable of then being hydrolyzed and fermented for the production of bioethanol; and on the other hand, the liquid phase, containing, in particular in aqueous solution, the formic acid, the lignins, and the hemicelluloses, constituting a second co-substrate, capable of then being hydrolyzed and fermented for the production of bioethanol.