The electrochemical reduction of four 4'-halogene-4-aminoazobenzene derivatives was studied in water/ethyl alcohol mixtures at various pH values using cyclic voltammetry (CV), sampled d.c. polarography (SCP), differential pulse polarography (DPP), chronoamperometry (CA) and constant potential coulometry (BE). The diffusion coefficients and the number of electrons transferred were determined using chronoamperometric Cottrell slope and ultramicroelectrode (UME) steady-state current. The transfer coefficient, heterogeneous rate constant and free energy of reduction of azobenzene derivatives were determined by Koutecky approach. Transfers of four-electron in acidic and two-electrons in basic media were established. Under the conditions employed, the reduction reaction was diffusion-controlled Also the substituent effect of halogens was examined.