Volumetric properties of mixed surfactants of Bis(2-ethylhexyl) sodium sulfosuccinate (AOT) and Ethoxylated-2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (Dynol-604) in aqueous solutions with various compositions have been studied at 298.15 K by density measurements. The apparent molar volumes, the partial molar volumes, the critical micelle concentrations, and the apparent molar volumes in the monomeric and micellar states of the binary mixed surfactants with various compositions were determined. Moreover, the results were used to calculate the micellar compositions, the excess free energies of mixing, the activity coefficients and the interaction parameter between two surfactants for the mixed micelles based on the Rubingh's formulism. (c) 2013 Elsevier Ltd. All rights reserved.