This communication reports a mechanism-based kinetics modelling for the dehydrogenation of ethylbenzene to styrene (ST) using Mg3Fe0.25Mn0.25Al0.5 catalyst. Physicochemical characterisation of the catalyst indicates that the presence of basic sites Mg2+O2- on the catalysts along with Fe3+ is responsible for the catalytic activity. The kinetics experiments are developed using a CREC Fluidised Riser Simulator. Based on the experimental observations and the possible mechanism of the various elementary steps, Langmuir-Hinshelwood type kinetics model are developed. To take into account of the possible catalyst deactivation a reactant conversion-based deactivation function is also introduced into the model. Parameters are estimated by fitting of the experimental data implemented in MATLAB. Results show that one site type Langmuir-Hinshelwood model appropriately describes the experimental data, with adequate statistical fitting indicators and also satisfied the thermodynamic restraints. The estimated heat of adsorptions of EB (64kJ/mole) is comparable to the values available in the literature. The activation energy for the formation of ST (85.5kJ/mole) found to be significantly lower than that of the cracking product benzene (136.6kJ/mole). These results are highly desirable in order to achieve high selectivity of the desired product ST. © 2012 Canadian Society for Chemical Engineering.