Abstract: The size distribution of dispersed droplets in W/O and (W/O)/W systems prepared in a standard stirred tank was measured by an Automatic Particle Analyzer and microphotography incorporated with an IBAS Image Analysis . system. Different emulsions were prepared at various stirrer speeds with two kinds of surfactants for the study. Mathematical models for estimating Sauter mean diameters of droplets for W/O and(W/O)/W dispersion systems, dp32 and d32, were developed respectively as equations (12) and (22), other than the effects of geometric parameter of vessel Dt, the operational parameter Nr and the properties of liquids usually considered, the effects of interfacial viscosity and emulsion viscosity were included in the equations. The equations fitted the experimental data quite well.