A new laboratory scale facility (fixed bed reactor) for the determination of solid fuel reactivity is presented. The reactivity is measured by burning samples of partially pyrolysed coals under dynamic conditions (rapid change of temperature and oxygen concentration). Mass conversion rate is determined from heat and mass balance equations, and the influence of boundary layer diffusion and chemical reaction rate on the measured reaction rate is evaluated. In the scope of a co-operative test, the reactivity of Gottelborn bituminous coal has been investigated by different research institutions. Despite of the different conditions in different laboratory scale facilities, a good correspondence of results was found. Moreover, three coals of different rank have been investigated. The kinetic constants of these coals are also given.