NOVELTY - Pretreating a lignocellulosic biomass comprises: (a) hydrolyzing biomass with an acid solution to obtain a liquid fraction-1 (7) containing hemicellulose and a solid fraction-1 (6) containing cellulose and lignin; (b) separating the liquid fraction-1 and solid fraction-1; (c) drying (8) the solid fraction-1; (d) boiling (10) the solid fraction-1 in the presence or absence of an organic solvent to obtain a solid fraction-2 and a liquid fraction-2 containing the hydrated inorganic salt; (e) separating the solid fraction-2 and the liquid fraction-2; and (f) optionally treating solid fraction-2.    USE - The process is useful for pretreating a lignocellulosic biomass (claimed), which is useful for producing biomass fuel, which is useful as fillers for vegetation or agricultural wastes such as wood or straw, and for producing glucose.    ADVANTAGE - The method is capable of easily pretreating the lignocellulosic biomass to cellulose.    DETAILED DESCRIPTION - Pretreating a lignocellulosic biomass comprises: (a) hydrolyzing biomass with an acid solution to obtain a liquid fraction-1 (7) containing hemicellulose in the form of hydrolysis products and acid, and a solid fraction-1 (6) containing cellulose and lignin; (b) separating the liquid fraction-1 and the solid fraction-1; (c) drying (8) the solid fraction-1; (d) boiling (10) the dried solid fraction-1 in the presence or absence of an organic solvent in a medium comprising at least one inorganic hydrated salt having a metal compound of formula (MXn.n1H2O) to obtain a solid fraction-2 and a liquid fraction-2 containing the hydrated inorganic salt; (e) separating the solid fraction-2 and the liquid fraction-2; and (f) optionally treating the solid fraction-2.    M = metal comprising 1-13 groups of the periodic table;    X = anion;    n = 1-6; and    n1 = 0.5-12.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a method.    Reactor (2)    Solid fraction-1 (6)    Liquid fraction-1 (7)    Drying solid fraction-1 (8)    Boiling solid fraction-1. (10)