A series of theoretical analysis and experimental measurements were done to analyze the characteristic of the apparent viscosity of oil-water unstable mixtures which display the similar distributions as the mixtures in pipeline flow. Based on the experimental results, it can be concluded that the unstable oil-water dispersed mixtures are always show the characteristic of non-Newtonian fluid. The shear rate has a great influence on the apparent viscosity, particular for the water-in-oil mixtures. The effect of dispersed phase volume fraction on the apparent viscosity of the unstable mixtures displays the similar rules as the stable emulsions. Also, the influences of the dispersed phase distribution and viscosity on the apparent viscosity were studied through the corresponded experiments systematically. Furthermore, a new kind of prediction model was obtained in the present study. The unstable and non-Newtonian fluid characteristics of oil-water two-phase dispersed mixtures were considered in this model to improve their range of application and the prediction accuracy. Moreover, this kind of apparent viscosity prediction model was validated by using the experimental data from some other literatures including different kinds of oils such as white oil and crude oil, and the average deviation was always less than 9% which was a great accuracy of apparent viscosity prediction.