Propylene glycol has a good ability informing microemulsions with oleic acid and Tween 80 and its aqueous solution has a good solubility of STZL which can form a concentration gradient. So oleic acid, Tween 80 and Propylene glycol were subsequently used as the oil phase, surfactant and cosurfac-tant for the formulation of microemulsions containing STZL in this study.