A theory was derived which describes the dependence of the size of dispersed droplets on the composition of compatibilized polymer blends in steady shear flow. The effect of droplets breakup and coalescence on the interfacial area available for molecules of a compatibilizer and, hence, on interfacial tension has been considered. Dependences of the droplet size on the volume fraction of the dispersed phase has been determined for the following cases: (i) constant density of a compatibilizer on the interface; (ii) all compatibilizer molecules are localized on thr interface; (iii) maximum density of a compatibilizer on the interface exists which is characteristic of the system under study. The shapes of the dependences of the droplet size on the amount of dispersed phase for these cases are different. They strongly differentiate if the total amount of a compatibilizer or the ratio of the amount of compatibilizer to that of dispersed phase is constant during an increase in volume fraction of the dispersed phase.