A theoretical model is proposed to describe the hysteresis of phase inversion and the effects of stirrer speed and physical properties on phase inversion. The model represents phase inversion as the structural instability of the equation of population balance in agitated liquid-liquid dispersion systems. Phase inversion experiments were performed on liquid-liquid dispersion systems composed of water and hydrocarbon mixtures whose densities were adjusted to that of water with carbon tetrachloride. Good agreement was demonstrated between the volume fraction of the dispersed phase estimated by the model and that obtained experimentally.