The micellar Gibbs-Duhem relation for two-component ionic/nonionic mixed micelles is presented in terms of the apparent bound amount to micelles. For simplicity, the ionic surfactant and a salt are both uni-uni valent electrolytes and have a common counterion species. Compared to the theory by D.G. Hall on the basis of a consideration on the Donnan equilibrium [D.C. Hall, J. Chem. Soc. Faraday Trans. 87 (1991)3529], the present approach is simple and unambiguous. Considering changes at constant temperature and pressure, the two approaches provide nearly identical results. (C) 2011 Elsevier Inc. All rights reserved.