Pelletized recovered solid waste fuel is often applied in gasification systems to provide feedstock with a stabilized quality and high heating value and to avoid the bridging behavior caused by high moisture content, low particle density, and irregular particle size. However, the swelling properties and the sticky material generated from pyrolysis of the plastic group components also tend to trigger bridging in the retorting zone. It is well known that the plastic group materials, which occupy a considerable proportion of municipal solid waste, can melt together easily even under low temperature. This study investigates the pyrolysis behaviors of typical recovered solid waste pellets, including the devolatilization rate, heat transfer properties, char properties, and swelling/shrinkage properties, in a small fixed-bed facility over a wide temperature range, from 900°C to 450°C. The results are also compared with those from wheat straw pellets, a typical cellulosic fuel. Moreover, the SEM images and BET analysis of the char structure are further analyzed to provide additional explanation for the mechanisms of swelling/shrinkage phenomena observed during heating.