The regioselectivity of electrochemical reduction of four trichlorobiphenyls (PCB 28–30 and PCB 37) was studied by cyclic voltammetry and bulk electrolysis. The number of stages and mechanism of electrochemical reduction of each of the examined substrate were inferred on the basis of the experimental electron transfer coefficients and calculated (DFT) bond lengths and potential energy surface sections. GC/MS analysis of the controlled potential electrolysis products showed that chlorine atom in the disubstituted ring of trichlorobiphenyls is reduced more readily than in the monosubstituted ring and that the rate of chlorine reduction changes in the series o-Cl > p-Cl > m-Cl.