NOVELTY - Producing (M1) levulinic acid and formic acid and, cellulose, a sugar product and/or bioethanol from biomass in formic acid-based cooking comprises: (a) cooking biomass in formic acid and washing with formic acid, washing it in water and de-esterifying; (b) reacting obtained cellulose pulp in formic acid solution to produce levulinic acid and formic acid; (c) separating levulinic acid and formic acid; (d) recovering levulinic acid; (e) returning formic acid to cooking; and (f) recovering part of cellulose pulp.    USE - The method is useful for production of levulinic acid, formic acid, cellulose, glucose, sugar product and/or bioethanol form biomass (claimed).    ADVANTAGE - The method: avoids utilization of extra inorganic catalysts, extraction agents, high enzyme dosages in the enzymatic hydrolysis and formic acid losses in formic acid cooking and extra formic acid; and reduces need for water separation; and is economic.    DETAILED DESCRIPTION - Producing (M1) levulinic acid and formic acid, cellulose, a sugar product and/or bioethanol from biomass in a formic acid-based cooking process, comprises: (a) cooking the biomass in formic acid and washing it with formic acid, washing it in water and then de-esterifying; (b) reacting at least part of thus obtained cellulose pulp in a formic acid solution to produce levulinic acid and formic acid under conditions comprising pulp consistency 15-330 g, preferably 15-250 g dry pulp/liter of formic acid solution, 10-90%, preferably 30-60% formic acid, temperature 160-220 degrees C and reaction time 2-7 hours; (c) separating levulinic acid and formic acid; (d) recovering levulinic acid; (e) returning at least part of the formic acid to cooking (a); and (f), recovering part of the cellulose pulp obtained in step (a) or leading it to enzymatic hydrolysis to produce a sugar product and to fermentation to produce bioethanol. INDEPENDENT CLAIMS are also included for:    (1) preparing (M2) cellulose, sugar product and/or bioethanol from biomass in the formic acid-based cooking, while simultaneously producing levulinic acid and formic acid, comprising: steps (a)-(e) as above per se; washing a second part of the cellulose pulp obtained in step (a) with water and recovering it or leading it to enzymatic hydrolysis; and    (2) producing (M3) glucose, levulinic acid and formic acid from biomass in the formic acid-based cooking comprising: (a2) cooking biomass in formic acid and washing the thus obtained cellulose pulp with formic acid; (a3) washing the cellulose pulp with water and desterifying; (a4) partial enzymatic hydrolysis on the thus obtained cellulose to produce glucose; (b1) reacting the non-hydrolyzed cellulose pulp from step (a4) in the formic acid solution to produce levulinic acid and formic acid under the conditions; and steps (c)-(e) as above per se.