According to Liljekvist and Kronberg [40], the minimum of CMC appears if the composition of the binary mixed micelle is almost the same as the binary mixture in the bulk phase and it is in accordance with the CMC determined experimentally by us. This minimum corresponds to ˛ = 0.8. For ˛ = 0.8, XM1a(TX-100) is only slightly lower than 0.8. However, at ˛ equal to 0.2, 0.4 and 0.6, the XM1a values are considerably higher than TX-100 mole fraction in the mixture with CTAB in the bulk phase. It is interesting that the synergetic effect inthe mixed micelle formation increases with the increasing alcohol concentration. The presence of ethanol in the aqueous solutions of the TX-100 and CTAB mixture causes also the CMC decrease at it slow concentration as it was mentioned above. Probably in the range of ethanol concentration in which the CMC decrease is observed,the ethanol molecules interact more strongly with the hydrophilic parts of CTAB molecules than those of water and there is a decrease of repulsive forces between these parts. The ethanol molecules can also affect the bonding of the counterion to the surface active cation.It should be reflected in the conductivity of the studied solutions,