A process for the flame retardancy of a biobased lignocellulosic material, characterized in that it comprises the following steps: - optionally steam explosion and/or bleaching of the biobased lignocellulosic material, - impregnation of the biobased lignocellulosic material, optionally steam-exploded and/or bleached, in or with an aqueous solution comprising from 0.5% to 7% phytic acid and from 1% to 22% urea, said percentages being expressed by mass relative to the total mass of the aqueous solution, - optionally drying the impregnated biobased lignocellulosic material until it has a moisture content ranging from 5% to 20%, said percentages being expressed by mass relative to the total mass of the impregnated biobased lignocellulosic material, - cooking the impregnated and optionally dried biobased lignocellulosic material, at a temperature ranging from 140°C to 200°C, and preferably from 140°C to 160°C, for a time ranging from 15 minutes to 5 hours and preferably from 30 minutes to 2 hours, the flame-retarded biobased lignocellulosic material thus obtained comprising a content of phosphorus originating from phytic acid ranging from 0.1% to 10%, preferably ranging from 0.3% to 3%, said percentages being expressed by mass relative to the total mass of the flame-retarded biobased lignocellulosic material, said process being further characterized in that the biobased lignocellulosic material used at the start has not undergone any chemical treatment other than that of possible steam explosion and/or bleaching. - optionally steam explosion and/or bleaching of the biobased lignocellulosic material, - impregnation of the biobased lignocellulosic material, optionally steam-exploded and/or bleached, in or with an aqueous solution comprising from 0.5% to 7% phytic acid and from 1% to 22% urea, said percentages being expressed by mass relative to the total mass of the aqueous solution, - optionally drying the impregnated biobased lignocellulosic material until it has a moisture content ranging from 5% to 20%, said percentages being expressed by mass relative to the total mass of the impregnated biobased lignocellulosic material, - cooking the impregnated and optionally dried biobased lignocellulosic material, at a temperature ranging from 140°C to 200°C, and preferably from 140°C to 160°C, for a time ranging from 15 minutes to 5 hours and preferably from 30 minutes to 2 hours, the flame-retarded biobased lignocellulosic material thus obtained comprising a content of phosphorus originating from phytic acid ranging from 0.1% to 10%, preferably ranging from 0.3% to 3%, said percentages being expressed by mass relative to the total mass of the flame-retarded biobased lignocellulosic material, said process being further characterized in that the biobased lignocellulosic material used at the start has not undergone any chemical treatment other than that of possible steam explosion and/or bleaching. the flame-retarded biobased lignocellulosic material thus obtained comprising a content of phosphorus originating from phytic acid ranging from 0.1% to 10%, preferably ranging from 0.3% to 3%, said percentages being expressed by mass relative to the total mass of the flame-retarded biobased lignocellulosic material, said process being further characterized in that the biobased lignocellulosic material used at the start has not undergone any chemical treatment other than that of possible steam explosion and/or bleaching.