The process of obtaining microcrystalline cellulose from flax fibers, which involves obtaining organosolv pulp in an environmentally safer method, followed by its treatment with a mixture of acids and hydrolysis, is explored. The proposed technology allows reducing the number of stages of processing plant materials, eliminating the use of more expensive chemicals and reducing the consumption of traditional reagents. SEM, XRD, sieve analysis and conductometric analysis were used to study organosolv pulp and microcrystalline cellulose parameters. The obtained microcrystalline cellulose has a sulfate ash content of 0.082%, a conductivity of 54 μSm/cm, a degree of polymerization of 186, which meet the requirements of the European Pharmacopoeia and can be used as a filler and binder in the chemical, pharmaceutical, food industries, and medicine.