Disclosed is a method for producing nanocelluloses from a cellulose substrate including cellulose fibers, the method including the following sequence of steps: —a step of enzymatic treatment of the cellulose substrate, by bringing same into contact with at least one cleaving enzyme, then—a step of mechanical treatment of the cellulose substrate subjected to the step of enzymatic treatment, in order to delaminate the cellulose fibres and obtain the nanocelluloses. The at least one cleaving enzyme is chosen from the enzymes belonging to the family of lytic polysaccharide monooxygenases (LPMOs) capable of achieving cleavage in the presence of an electron donor. Also disclosed are the nanocelluloses obtained according to the method.