FIELD : technological processes.SUBSTANCE : invention relates to chemical treatment of cellulose, in particular to methods of producing ultrafine particles and hydrosols of nanocrystalline cellulose, and can be used in pharmaceutical, food, perfume and other industries for production of organic nanoparticles with ordered structure, biocompatible materials based thereon, rheological modifiers and thickeners, plastics fillers, biodegradable polymer materials and composites, paint stabilizers, fibers and emulsions. Method of producing nanocrystalline cellulose particles by catalytic solvolysis in an organic medium in the form of an aqueous dispersion includes controlled destruction of powdered cellulose obtained from softwood or hardwood, or linen, or cotton, extraction, purification of the end product, wherein decomposition is carried out by catalytic solvolysis of cellulose material in a mixture of acetic acid, octanol-1 and phosphotungstic acid, wherein phosphotungstic acid is taken in amount of 0.2–0.3?% of molar relative to anhydroglucose cellulose unit, the ratio of acetic acid/octanol-1 is 10 : 1 volume parts, cellulose destruction process is carried out at the boiling point of the obtained mixture for 40?minutes, while adding a hydrogen peroxide solution in amount of 0.05?% of the volume of liquid in system every 5?minutes.EFFECT : improved method of producing NCC from different types of celluloses with lower consumption of reagents and reduced duration of de-structuring process.3 cl, 1 dwg, 1 tbl