Proton transfer complexing equilibrium in aqueous media between p-nitrosalicylic acid and ethylenediamine has been studied in presence of CTAB, SDS, TX-100 and PEG, where CTAB and SDS have been observed to enhance the reaction whereas, TX-100 and PEG have suppressed it. Salts like KCl and NaCl have got antagonistic effects on the activities of CTAB and SDS. The proton transfer phenomenon can help determining the cmc of the additives. The equilibrium constants of the process have been determined and the standard thermodynamic parameters, ΔH°, JG' andΔ S° have been derived. The process has shown ‘isothermodynamic’ linear enthalpy-entropy relationship.