Modeling is a useful tool for the design, scale-up and control of bioreactors. In the present work a kinetic model was proposed for the microbial growth in the solid-state bioreactors. In this model, despite the tact that the growth rate depends on the current temperature of bioreactor, it also depends on the past temperatures that the organism has previously undergone. Model predictions were compared to literature data for the growth of Aspergillus niger on wheat bran and agreed reasonably with experimental results. Also in this study, to modeling the temperature gradients in packed-bed solid-state bioreactors, two dynamic heat transfer models namely lumped and distributed were considered and compared. The results showed that the predictions of the distributed model have better agreement with literature experimental data than lumped model. (c) 2008 Elsevier B.V. All rights reserved.