The present work deals with the use of a torus mixer for the formation of liquid-liquid dispersion. The objective is to determine the performance of the torus reactor to form the primary emulsion of the microencapsulation process of an active product by a solvent evaporation technique. The encapsulated product is dissolved in an aqueous phase, which is emulsified into a solution of the polymer in methylene chloride to form a water/oil emulsion. The methylene chloride is gradually removed from the droplets by evaporation. Hard microcapsules are obtained when the solvent is completely removed. The formation of the water/oil primary emulsions is the key step to control the size distribution of the microcapsules. The characteristics of the dispersed phase of the water-in-oil emulsion produced in a torus mixer in batch and continuous conditions is determined by an optical method based on the use of the microscope connected to a CCD camera. The flow inside the torus mixer is directly linked to the rotation speed of the impeller. The effect of the rotation speed of the impeller and the dispersed phase volume fraction of the liquid-liquid dispersion is analyzed. The experimental data are expressed by a correlation giving the mean droplet diameter in function of the Weber number and dispersed phase concentration. The influence of the superimposed throughput, for the continuous process, on the size distribution of the dispersed phase is also taken into account.