The miscibility and interactions between components in mixed adsorbed films and micelles containing zwitterionic (dodecyl sulfobetaine-DSB) and cationic (dodecyltrimethylammonium bromide) or anionic (sodium dodecyl sulfonate) surfactant, respectively, have been investigated. The Molecular interactions have been quantified by the values of the excess free energy of adsorption (&UDelta; G(S, Exc)) and micelle formation (AGM,Exc). The obtained results indicate nonideal behavior of the investigated mixtures since the Values of &UDelta; G(S,Exc) and &UDelta; G(M,Exc) are negative. Moreover, it has been found that DSB interact more strongly with anionic surfactant as compared to cationic surfactant owing to different structure of mixed monolayers and micelles. © 2004 Elsevier Inc. All rights reserved.