Abstract: The present innovation consists of the use of a reagent solution (FINAL COOKING ACID) where ammonium magnesium bisulphite is the active chemical. This new process is particularly useful to those industrial plants where the cellulose pulp is obtained by the magnesium acid process. The present innovation consists of the introduction of ammonium ions in the cooking acid used in such plants (initial cooking acid). The final cooking acid is obtained by the reaction of the initial cooking acid with ammonium hydroxide. Experimental results show the superiority of the present innovation over the magnesium acid bisulphite pulping process which is expressed by production of cellulosic fibres with higher mechanico-physical index values, decrease in the percentage of uncooked material, increase in wood yield and less environmental impact.