This article presents a physically-based mathematical model for the description of particle wetting and of temperature and concentration distribution in fluidized bed spray-granulation. The air humidity, air temperature, degree of wetness of the particles, liquid film temperature and particle temperature can all be calculated while taking into account the apparatus wall, the influence of the environment and of heating surfaces, which might be implemented in the fluidized bed. The effects which the unsteady start-up and shut-down procedures, as well as the alteration of process parameters, such as the mass flow rate of the liquid sprayed in with a jet and the liquid temperature as well as the fluidizing airflow rate and air temperature, have on the balance quantities, can be simulated. The bed mass and particle diameter growth in discontinuous granulation are taken into account and the two-dimensional calculation of the temperature and concentration distributions were carried out for the steady, continuous fluidized bed spray-granulation. The validation of the model was carried out at the Institute using a semi-industrial fluidized bed plant with a diameter of 0.4 m in the bed area. Dimensionless constants are proposed for the evaluation of the process.