Abstract: The invention relates to a process for the delignification of unbleached chemical pulp, comprising the following stages:(a) oxidation of the unbleached pulp with a peroxide, in an alkaline medium with a % ratio of peroxide/pulp with respect to the Kappa index of said pulp which may vary between 0.01 and 0.1 and a pH kept at between 9 and 12, the said oxidation stage being followed by(b) mechanical pressing of the oxidized pulp, with recycling of the extraction effluents from the pressing stage,partly above the oxidation stage,partly below the oxidation stage, with a view to ensure the prior dilution of the pulp oxidized before the pressing,and if necessary partly towards the wash of the unbleached pulp.Advantages: A reduction in the quantities of reagents to be used, a saving of heat energy and a reduction of the pollution.