The results of the study of the coagulation kinetics of graphite nanoparticle suspensions in aqueous AlCl3 and Th(NO3)4 electrolytes are presented. Electro-optical effects in disperse systems containing graphite particles allow to reliably investigate the coagulation kinetics in such systems. A method based on the analysis of changes of electro-optical effect relaxation dependencies in the process of coagulation was developed. The dependencies of the electrokinetic potential on the concentration of electrolytes are presented. Coagulation in such systems is observed if electrokinetic potential of graphite particles does not exceed 5 mV. At the isoelectric point, the fast coagulation theory is in good agreement with the observed processes of formation of aggregates from graphite particles. The conducted studies confirm the conclusion that the formation of aggregates from graphite particles with lyophobic surface is mainly influenced by the valence of the ions that determine the surface charge, and their other characteristics are of secondary importance. Display omitted •Aqueous graphite colloid with particle size 20–400 nm was studied.•Coagulation kinetics of graphite nanoparticles at isoelectric point were studied using electro-optic technique.•The influence of multivalent salts AlCl3 and Th(NO3)4 is studied, compared and discussed.•At the isoelectric point, the formation rate of pair aggregates from particles corresponds to the theory of fast coagulation.