Abstract: AimTo prepare the microemulsion of vinpocetine in order to increase solubility and its in vitro transdermal delivery by using appropriate proportion of oil, surfactant (S), cosurfactant (CoS) and water. The formulation of proportion was optimized. The physicochemical properties and the skin irritation of the microemulsion was studied. MethodsPseudo-tertiary phase diagrams were prepared to obtain the concentration ratio of components of the microemulsion. Using simplex lattice method, the formulation of microemulsion was optimized and the physicochemical properties including pH, viscosity, refractive index, conductivity and particle size distribution were examined. The MTT method was applied to test the skin irritation of the microemulsion on the Hacat cell. ResultsThe diagrams showed that the areas of O/W microemulsion increased with the increasing ratio of surfactant to cosurfactant (S/CoS). The predicted values from simplex lattice system were close to that of the experiment. The property of optimized microemulsion showed to be stable behavior and not irritant to Hacat cell. ConclusionThe drug solubility and in vitro perscutaneous permeation flux of the optimized microemulsion was improved significantly and the irritation study showed that optimized microemulsion was safe as an ideal transdermal delivery system.