In the present article, a comprehensive mathematical model for single particle propylene polymerization mainly extended from polymeric multigrain model (PMGM) and multigrain model (MGM) has been developed to describe kinetic behavior, molecular weight distribution, monomer concentration, degree of polymerization and polydispersity index (PDI) for slurry-phase propylene polymerization using heterogeneous Ziegler-Natta catalysts. The modified model gives a more valid mathematical description by accounting for the monomer diffusion phenomena at two levels, namely, taking the effect of monomer diffusion at both the macro- and microparticle levels into account, and the latter is aside from the subject under consideration by PMGM. It has been observed that the present model can predict higher values of polydispersity index (PDI about 6-25) with obtaining some results which are more applicable to the conditions existing in most polymerizations of industrial interest such as the reasonable monomer concentration at the center of particles throughout polymerization process and the effect come nearer to the actual physical process of the initial radius of macro- and microparticles as well when using single-site, non-deactivating catalyst. Further, special attention is also paid in this article to discuss the computational rate, which is the most disadvantage of MGM. It has been shown that the significant computational time saving is also acquired by employing the novel solution methodology. (c) 2005 Elsevier Ltd. All rights reserved.