This paper describes the development and predictions of an engineering model that depicts the two-phase flow within an internally mixed air-assisted liquid atomizer. The main objective of this study is to develop an analytical tool that could be used in the design of improved internally mixed injectors and to predict the injector's flow and spray characteristics under different operating conditions. The developed model assumes that the formation of liquid drops, due to the interaction between the air and liquid flows, occurs inside the injector in an internally mixed atomizer. Basic conservation equations, along with appropriate boundary conditions, are used to model the two-phase air-liquid flow inside the injector. A critical Weber number criterion is used to estimate the mean size of the droplets being produced in the process. A unique solution procedure, using transformation and elimination of variables, is developed to solve this set of equations, which can be readily implemented on a PC. The liquid flow rates and mean droplet sizes, predicted by the model, are compared with the experimentally obtained results and they are found to be in good agreement with each other.