The optimization of the separation resolution for a group of N-phenylpyrazole derivatives in micellar electrokinetic chromatography (MEKC) as a function of the separation buffer composition (surfactant and organic modifier concentration) has been performed. In order to achieve our purpose, the first step has been the prediction of the migration times of the electroosmotic flow (t(0)) and micelles (t(m)), and the retention factors of solutes (k), as a function of surfactant (sodium dodecyl sulfate) and alcohol (n-propanol or n-butanol) concentrations, by means of empirical equations. Also, some physicochemical models have been applied to relate the retention factors to the surfactant and the organic modifier concentrations in order to optimize the separation resolution and to increase our knowledge of the separation process. Finally, a comparison of the resolution optimization through the use of the physicochemical and empirical models selected has been made in order to obtain the optimum separation buffer composition for the separation of a group of 17 N-phenylpyrazole derivatives as test solutes.