Solutions of the 2% mixtures of Na-dodecyl sulfate (SDS) and cosurfactants (lauryl alcohol, lauric acid, and cetyl alcohol) in different molar ratios (1/1 and 1/2) have been prepared and the electrical conductivity-temperature dependence was investigated by means of an electronic conductometer. When SDS/cosurfactant mixed solutions are slowly heated or cooled (2 degrees C/min), conductometric curves reveal an inflection at the phase transition temperatures. These temperatures are in the connection with the melting points of the cosurfactants, but depend also on the surfactant/cosurfactant molar ratio, Higher values of the specific conductivities are detected by heating the freshly prepared mixed solutions than by heating the aged ones. Specific conductivities of the aged solutions indicate that during the phase transformation, single components (surfactant and cosurfactant molecules) do not separate from the liquid crystals. Electrical conductivities of SDS/CA mixed solutions are higher than the conductivities of SDS/LA and SDS/LAcid solutions through the whole temperature interval investigated. This suggests some difference in the internal structure of the dispersed phases in these solutions, which gives different ion concentrations in the continual phase.