To improve the skin permeability of piroxicam, a new oil-in-water microemulsion containing 0.5% piroxicam was developed. Among various oils investigated for their suitability as an oil phase for the microemulsion system, oleic acid showed both excellent solubility and skin permeation enhancing effect for piroxicam. Microemulsion existence ranges were identified through the construction of the pseudo-ternary phase diagram. The effect of the content of oleic acid and the ratio of the surfactant/cosurfactant on skin permeation of piroxicam were evaluated with excised rat skins. The optimum formulation with the highest skin permeation rate (47.14 microg/cm2/h) consisted of 0.5% piroxicam, 10% oleic acid, 60% Labrasol/ethanol (1:5) and water.