A simple model is proposed for sulphation of CaO-based sorbents in fluidized bed combustion. The model focuses on the sintering effect of CaSO4 product on the sorbent particles. The resultant equation is validated with experimental data and is seen to describe the time dependence of the sulphation well. It is also shown that for short sulphation times the equation becomes equivalent to that of an existing model but gives a better description of the sulphation behavior over a long sulphation period.