Multiple studies by several independent experimental methods indicate that alcohol molecules aggregate in aqueous solutions[16–24]. It is also reflected by the surface tension [25], density(Fig. 1 and Tables S1–S4) and dynamic viscosity isotherms (Fig. 2 and Tables S5–S8). On these isotherms there were found the break points which suggests that at a given ethanol concentration, the aggregation of its molecules takes place [16–24]. The values of the mole fraction corresponding to the aggregation of ethanol molecules determined on the basis of the surface tension isotherms are in the range from 0.154 to 0.162 and they are practically similar to those obtained from the density and dynamic viscosity isotherms Fig.(Table 2). The values of the critical aggregation concentration (CAC)of ethanol obtained from the isotherms of the surface tension, density and dynamic viscosity of the aqueous solutions of the TX-100 and CTAB mixture with ethanol are close to those determined by Kahlweit et al. [17] at 25◦C, but lower than those obtained by Zanaand Eljebari [16], and Hayashi and Udagawa [18] from the properties of the aqueous solutions of “pure” ethanol. Some differences between the values of CAC obtained by us and those of Zana and Eljebari [16] result probably from the fact that CAC is not one pinpoint value but it is a range of the concentration in which the aggregates are formed and each method can give a different CAC value.The data obtained by Zana and Eljebari [16] were based on the fluorescence measurements and the CAC was obtained at the temperature (298 K) different from that used in our experiments (293 K).