Abstract: We demonstrate that the electrooptical method can be used to study the coagulation of liquid nanodisperse systems, in particular, colloids and suspensions. Two electrooptical effects have been used—one dependent and one independent of the polarization of light passing through the system in the electric field. The results of study of the coagulation kinetics at its early stage, associated with the formation of pair aggregates from graphite particles suspended in AlCl₃ and Th(NO₃)₄ aqueous electrolytes are presented. We show that the systems are stable in a wide range of electrolyte concentrations and lose their stability in a narrow range in which the electrokinetic potential of particles does not exceed 5 mV. We show that the electrooptically determined dependences of the particle concentration on the coagulation time at the isoelectric point agree well with the Smoluchowski theory of rapid coagulation.