Micelle formation of sodium dodecyl sulphate (SDS) and Lithium dodecyl sulphate (LDS) in aqueous solutions has been studied. Critical micelle concentration (CMC) of both surfactants has been determined by surface tension, refractive index, electrical conductance, viscosity and UV spectroscopic methods. Effects of different alcohols (eg. ethanol, propanal, butanol) on the CMC of both SDS and LDS are discussed. It is shown that no micellization of these surfactants occurs in pure alcohols.