The kinetics of vapour phase aminocylisation of acetaldehyde, formaldehyde, and ammonia over deactivating HZSM-5 catalyst is studied. A series-parallel reaction scheme has been employed in which coke formation from its precursors has been lumped. Applying the concept of separable kinetics, the catalyst deactivation and reaction kinetics unconstrained and constrained by it are studied independently. Employing experimental time on stream studies, the rate of catalyst decay has been computed from the latter. A catalyst deactivation function based on experimental decay of its activity has been evaluated separately. Its magnitude and trajectory matched well with that of the computed catalyst decay function. It facilitated to obtain a direct relationship between coke formation and product distribution as a function of time on stream for aminocyclisation. An attempt has also been made to study the regeneration characteristics of the catalyst.