The forming mechanism of microemulsion of sodium dodecyl sulfonate, alcohols, water and isooctane was studied, with particular emphasis on the effect of molecular weight and concentration of alcohols. Phase diagram of the four components, alcohol, sodium dodecyl sulfonate, water and isooctane, was used as a means of study, through which the microemulsion regions were deter-mined. Phase diagram of sodium dodecyl sulfonate/n-pentanol/isooctane/water system at km = 2 (km = Wn-pentanol / WSDS ) is presented. The variation of conductivities of different microemulsion samples with water was measured. From the conductivities we investigated a change in structure from water droplets in oil (W/O) at low water content to liquid crystal at intermediate water content and a struc-ture of oil droplets in water (O/W) at high water content. The forming mechanism of microemulsion of sodium dodecyl sulfonate, alcohols, water and isooctane was studied, with particular emphasis on the effect of molecular weight and concentration of alcohols. Phase diagram of the four components, alcohol, sodium dodecyl sulfonate, water and isooctane, was used as a means of study, through which the microemulsion regions were deter- mined. Phase diagram of sodium dodecyl sulfonate / n-pentanol / isooctane / water system at km = 2 (km = Wn-pentanol / WSDS) of conductivities of different microemulsion samples with water was measured. From the conductivities we investigated a change in structure from water droplets in oil (W / O) at low water content to liquid crystal at intermediate water content and a strucure of droplets of oil in water (O / W) at high water content.