The prediction of slurry viscosity for the suspensions with and without particle size distribution has become possible by using the suspension theology model proposed in this study. The viscosity prediction model is based on Simha's cell model, which is applicable to completely dispersed systems. It was verified experimentally that the Simha's model was able to predict the slurry viscosity for the case of the suspensions with particle size distribution. The present suspension theology model adopted the assumption that the effect of agglomeration appeared only for the cluster formation with the minimum sized particles, and the other larger particles were completely dispersed. The same type of theology model was previously proposed by one of the present authors, but the model was modified to give more accurate viscosity predictions. The present model makes the assumption that multi-breakup of inter-particle bonding occurs when a cluster breaks into two parts under a simple shear flow. It is demonstrated that the present model combined with the Simha's cell model can be successfully used to predict the theological behavior of slurries.