To study the effect of cation-exchange layer thickness on the electrochemical and transport characteristics of bipolar membranes (BPM), asymmetric BPM with varied cation-exchange layer thickness (of 10, 30, 50 and 70 mu m) were investigated. High influence of BPM monopolar layers thickness on its selectivity had been shown. This fact is non-trivial in relation to monopolar ion-exchange membranes as their selectivity does not depend on their thickness. At the same time, increase or decrease in the thickness of BPM monopolar layers can increase products purity or, on the contrary, combine ion transport and pH shift functions.