A mathematical model was developed to describe the drying process of microorganism pellets in a fluidized bed dryer. The modeling of heat and mass transfer between air and the pellets in fluidized bed dryers is based on application of temperature and diffusion equations inside the pellets. These equations were nonlinear partial differential equation. Robin boundary condition was selected to solve nonlinear differential equations. In this model, the microorganism pellets are assumed to be non-Shrinking and homogenous. The material forms were cylindrical geometry. The baker yeast, the microorganism Saccharomyces cerevisiae was used to test the model in this study. The experimental results of the drying process were compared to the mathematical model predictions. As to the results of comparison, this model was shown very good agreement for batch fluidized bed drying of baker yeast.