Fluidised bed granulation (FBG) is a particle size enlargement technique which is widely employed in industry. Modelling of FBG is important in order to understand, control and optimise the process. In literature, population balance modelling (PBM) which is based on population balance equations (PBEs) is a common tool to model the processing of these particulate systems. However, the solution of PBEs is not straightforward except for relatively simple cases. In this paper, Markov chain simulation is introduced in order to model and analyse the particle size enlargement process in fluidised bed granulation where aggregation and breakage occur simultaneously. For the study, the size enlargement process of granules based on glass beads is examined. 10 g PEG (poly ethylene glycol) with 60% concentration is used as the binder for a 200 g batch. The results show that Markov chains are an efficient tool to model the granulation process. Particle size enlargement and the shape of particle size distributions during the granulation process have been estimated within acceptable errors.