A method of production of lignin and hemicellulose from a plant lignocellulosic material includes (a) contacting a plant lignocellulosic material with an extraction solution during more than 2 hours at a temperature between 95° ° C. to 110° C., thereby obtaining a solid fraction and a liquid fraction, (b) separating the solid fraction and the liquid fraction, (c) concentrating the liquid fraction so as to obtain a concentrated liquid fraction, (d) mixing equal parts by weight of water with the concentrated liquid fraction so as to obtain a suspension comprising solid particles in suspension in a liquid medium, (e) separating the particles and the medium of the suspension, (f) recovering the particles of the suspension thereby obtaining a fraction comprising lignin called lignified fraction, (g) recovering the medium of the suspension thereby obtaining a fraction comprising hemicellulose called hemicellulosic fraction.