This paper presents the results of an investigation carried out to experimentally determine the deactivation constant of a fluid catalytic cracking (FCC) process. Kinetic modeling was performed using a four-lump model and an experimentally determined deactivation constant. Significant improvement was achieved in predicting the product gasoline, gas and coke yields compared to the yields predicted by models using a theoretical deactivation constant. Activation energies for each reaction are reported and compared with the literature values.