Calculation of the thermodynamic characteristics of the interface of two immiscible electrolyte solutions (ITIES) was carried out using the self-consistent mean-held theory for adsorption and/or aggregation developed by Scheutjens and Fleer (1). The effect of tetraalkyl-ammonium-halogenid salts on the interfacial tension of 1,2-dichloro-ethane-water system was calculated for different alkyl groups, hence for different amphiphilic salts. For comparison, experimental determination of the interfacial tension was also carried out using a dynamic drop-weight method. It is found that the interfacial tension is significantly reduced due to the presence of the salts and the effect is larger for larger alkyl groups. Qualitative agreement was found between the calculated and the measured data. The model calculations showed also that the concentration of water near the interface may change non-monotonously.