Powders with the correct amount of a liquid binder can be formed into agglomerates by vibrating, shaking or paddle mixing. Rotating drums or disks are commonly used in industry. The break-up process of the drops of the binding liquid and the kinetics of the powder agglomeration affect the granule size distribution in the agglomerate. Generally, mathematical procedures are required to estimate such size distributions. A theoretical model is presented in this study to emphasize the major system parameters affecting the particle size distribution during agglomeration. First, an analytical relationship is derived to represent the changes in the droplet volume with time. Then, Focker-Planck equation is used to predict the granule size distribution in an agglomeration process. The model predictions are compared with the experimental data, The results indicated that the model predictions and the experimental data are in a good agreement.