In order to produce a clean producer gas, the air gasification of dried sewage sludge was conducted in a two-stage gasifier that consisted of a bubbling fluidized bed and a tar-cracking zone. The kind and amount of bed materials, the kind of additives in the upper-reactor, and the moisture content in the sewage sludge were selected as operating variables in order to investigate their effects on the development of the producer gas characteristics. In our experiments, the gasification of a dried sewage sludge sample containing 30 wt.% of moisture with a combination of calcined dolomite as the bed material and activated carbon in the tar-cracking zone removed the most tar and produced the highest hydrogen concentration. The total tar removal efficiency and the H-2 content in the producer gas from the sample noted above reached 88.4% and 32.1 vol.%, respectively. The LHVs of all the producer gases were high with values above 7 MJ Nm(-3). Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.