The physicochemical properties of the initial components, poly-N,N-dimethyl-N,N-diallylammonium chloride, lignosulfonate, and polyelectrolyte complexes based on them, were studied. Optimal conditions and initial compounds were selected for polymerization of poly-N,N-dimethyl-N,N-diallylammonium chloride. The experiments were modeled with the STATISTICA 13 software package. The results from determination of the particle size of the samples of poly-N,N-dimethyl-N,N-diallylammonium chloride by laser diffraction are presented. Comparative analysis was made of the composition of the functional groups by means of the IR spectra of lignosulfonate sulfite and neutral sulfite methods of cellulose production A comparative analysis of the composition of the functional groups based on the IR spectra of lignosulfonate in the sulfite and neutral-sulfite method of cellulose production was undertaken. Potentiometric titration was used to study possible complexation of the lignosulfonate with Fe(77) ions and a polyelectrolyte complex based on modified lignosulfonate and poly-N,N-dimethyl-N,N-diallylammonium chloride. The effect of samples of the obtained polyelectrolyte complex on the filtration properties of drilling mud under aggressive temperature conditions was studied.