The free-liquid electrophoresis combined with radiotracer method was used for the analysis of bonding of cadmium with humic substances in aqueous solutions. It has been shown that the method enables the determination of the abundance and/or mean electrophoretic mobility of cadmium húmate complexes and can bring new possibilities into the study of cadmium bonding with humic substances. The abundances and negative mobilities (charges) of cadmium complexes with two industrial humâtes and 3 molecular size fractions of one of the humâtes increased from pH 4 to pH 8 and with increasing molecular weight of the fraction.