A simple and rapid micellar electrokinetic chromatography (MEKC) method was developed for the analysis of an antiviral drug, oseltamivir, and its hydrolyzed product in Tamiflu capsules. Background electrolytes consisted of boric acid 10 mM, pH 10, and sodium dodecyl sulphate (SDS) 40 mM. The limit of detection (LOD) and limit of quantification (LOQ) of oseltamivir were 1.7 and 8.0 microg/ml, respectively. MEKC sweeping in a high electroosmotic flow environment for neutral analytes was also utilized to improve the sensitivity of the assay. In MEKC-sweeping mode, a buffer comprising boric acid 30 mM, pH 10, and SDS 50 mM was used. A 17-fold increase in detection sensitivity was achieved with the MEKC-sweeping method compared with the MEKC mode. Unlike in MEKC, the LOD and LOQ for oseltamivir were 0.1 and 0.3 microg/ml, respectively, using the MEKC-sweeping method. Both methods were successful in determining oseltamivir concentration in its capsule formulation, and the MEKC-sweeping method was capable of determination of the drug at lower concentrations. The hydrolyzed product of oseltamivir (oseltamivir carboxylate) was also detected using the MEKC method. Our observations revealed that the prodrug could be hydrolyzed to the active compound at alkaline pH within ca. 60 min.