A mathematical model is proposed for the urea prilling process of a commercial plant. In this model the prilling process has been simulated by simultaneous solution of the continuity, hydrodynamic, mass and energy transfer equations. Particle trajectory, temperature and moisture distribution of the particles and of the cooling air along the height of the tower was calculated from the mathematical model. The air temperature profile resulted from the model was compared with the profile from the urea plant. The model predicted data were consistent with the plant data indicating the validity of the model. The result of this work showed that an increase in heat removed from the particles would improve the characteristics of the product urea.