Budesonide belongs to Class II in the Biopharmaceutics Classification System (BCS) for its high permeability and poor aqueous solubility. The purpose of this study was to improve the solubility and dissolution rate of budesonide using an o/w microemulsion system in order to develop a nasal formulation. Based on the results of the solubility study and pseudo ternary phase diagrams, microemulsions of about 80 nm in mean diameter were formulated using isopropyl myristate and Labrasol$^{(R)}$ as an oil phase and a surfactant, respectively. Solubility of budesonide in the microemulsions increased up to 6.50 mg/mL, which is high enough for a nasal formulation. In vitro release profiles of budesonide significantly increased from the microemulsions compared to that of the budesonide powder. These results suggest that the microemulsions of budesonide could further be developed into a clinically useful nasal formulation.