The article presents the results on the thermal processing of the samples of flax production - flax shive and the cellulose residue of flax shive. Experimental data on the conversion of selected samples of flax production waste obtained on a laboratory installation of slow pyrolysis in a temperature range of 500-750 ? are presented. The composition of gaseous pyrolysis products has been studied in detail and the main content of methane, hydrogen, and carbon oxides in the course of the process have been determined. Data on the composition of liquid products of pyrolysis of selected samples of plant biomass using the method of gas chromatography-mass spectrometry are presented. As part of the work, elemental analysis of samples of solid carbon-containing residues for the studied samples of flax and cellulose residue was carried out, and an analysis was carried out by the method of low-temperature adsorption of nitrogen.