Recently, several studies have been performed for the substitution of the conventional short chain alcohol by butyl lactate as a cosurfactant on the preparation of microemulsions. The effort is attractive since butyl lactate can be obtained from renewable resources and may be used as a safe and biodegradable product in the cosmetic and the dermal drug delivery. In the present work, the phase behavior was investigated and the characterization study was performed for the SDS microemulsion system which employed butyl lactate as a cosurfactant. The butyl lactate system provided the wider microemulsion region than the system for pentanol. The results of conductivity study indicated that the ratio, r = [cosurfactant]/[SDS] at the interface, was varied from 1 to 2 depending on the composition of microemulsions and the results revealed that the area occupied by butyl lactate at the W/O interface was about 33 A(2..)