Process for defibering a fibrous raw-material. According to the process a raw-material is contacted with a pulping liquor that contains an organic solvent for producing a defibrated fibrous raw-material. Cooking liquor contains by its weight about 0.01 to 10 % of hypo-phosphoric acid or corresponding reducing phosphoric acid derivative. A remarkable high yield is obtained by the process and cooking has been noted to have an effect activating the fibrous material. The fibrous material has good mechanical properties, it reacts easily with functionalizing enzymes and it is easily hydrolysable in to sugars e.g. by means of enzymes.