Method for rate constants determination of ligands substitution reactions in coordination sphere of metals has been developed. The rate constants of aquatation reactions of pentaquochromyl chloride (III), dichlorotetraquochromyl chloride (III), and perchlorate pentamino (methyl sulfoxide) cobalt (III) at the temperatures 20-60 C have been determined by electrodialysis. The method is particulary attractive for the cases where solutions of initial reagents or products do not obey to Buger-Lambert-Beer`s law, or extinction coefficients of a starting and resulting complexes slightly differ in their values.