Combustion characteristics of dried sewage sludge was investigated by using a vertical laminar flow furnace. The reaction rate were compared with that of coal. The combustion process of sewage sludge proceeded in two steps-the primary preheating and the following volatile matter combustion. The oxygen concentration had no effecs on ignition delay and burn-out time. The fractional conversion of the sludge including high polymer as a cohesion glue increased with increasing the particle size at the same residence time. On the contrary, the particle size had no influence on fractional conversion of the sludge including slacklime as a cohesion glue. It was found that a surface reaction model was applicable to sludge with high polymer whilst a volume reaction model (first-order reaction model) was applicable to coal and sludge with slacklime respectively. The combustion rate of sludge increased rapidly over Tg=1200°C where the activation energy also increased from 8.6kcal/mol to 48.5kcal/mol. The over-all combustion rates of sludge were nearly equal or larger than those of coal.