The purpose of this study is to develop a modified sorbent of flax waste and investigate its sorption properties towards Cu (II) ions. The authors conducted the modification in two steps. The first step was oxidation of flax fibre cellulose with sodium metaperiodate to dialdehyde cellulose, the second one was the addition of taurine to increase the sorption characteristics of the modified sorbent. The paper presents the conditions for the periodate oxidation reaction of flax fibre and the treatment of the resulting dialdehyde cellulose with taurine. We determined the sorption characteristics of the modified sorbent in comparison with the original flax fibre. Kinetic studies allowed us to establish the time of reaching sorption equilibrium in the heterophase system ‘aqueous solution of metal salt-sorbent’ and determine the reaction order using pseudo first and pseudo-second order kinetics models. The authors processed the sorption isotherms obtained during the experiments using the Langmuir model. The maximum sorption capacity increased by 3 times compared to the original flax fibre. IR spectroscopy confirmed the improvement of equilibrium and kinetic characteristics of flax fibre occuring as a result of the appearance of new sorption centres in its structure.