The present work is devoted experimentally to determine the behavior of the flow of both air and water in an internal mixing air-assisted atomizer with swirling coaxial liquid, pointing the attention on the optimization of some geometrical parameters. Some experiments have been performed for air central channel diameter and coaxial liquid port, as well as for several experimental conditions (air and water pressures), this is an important result that will help in the optimum design of this type of atomizer.