The mixed adsorption of azathioprine and Triton X-100 or Tween 80 at the mercury/ chlorates(VII) interface was described. The differential capacitance of the double layer "C" _"d" at the Hg/ basic electrolyte interface was measured using the electrochemical impedance spectroscopy. The potential of zero charge "E" _"z" was determined applying streaming mercury electrode and the surface tension at the potential of zero charge "γ" _"z" was measured by the method of the highest pressure inside the mercury drop. The changes of determined parameters in the function of the supporting electrolyte concentration point with the participation of 〖"ClO" 〗_"4" ^"-" ions in the adsorption process, as well as the electrostatic interactions between the dipoles of H2O and azathioprine– Triton X-100 or azathioprine – Tween 80 in the double layer are shown.