A theoretical model of phase inversion using structural instability of population balance in agitated liquid-liquid dispersion is proposed. The model describes the hysteresis of phase inversion and the effects of stirrer speed and physical properties on phase inversion. Phase inversion experiments were performed on liquid-liquid dispersion systems composed of water and hydrocarbon mixtures. The physical properties of the organic compornent were varied by mixing the hydrocarbon with carbon tetrachloride. The volume fractions of dispersed phases of various densities, viscosities and interfacial tensions were measured and found to show good agreement with those estimated by the model.