This paper represents the effect of Dimethyl sulfoxide on the micellar behavior of SDS in aqueous mixtures of tryptophan. The critical micellar concentration (CMC) of SDS is represented in terms of mole fraction unit (XCMC) and was determined at different temperatures i.e. (293.15, 298.15, 303.15 and 308.15 K) using electrical conductivity method. The dependence of XCMC on temperature and concentrations of tryptophan and DMSO reveals the presence stronger intermolecular interactions between tryptophan and SDS. The negative value of ΔGo m represents the spontaneity of the system. The positive values of entropy of micellization ΔSm o indicate the dominance of hydrophobic interactions in tryptophan-SDS system.