Lignite and sewage sludge were co-pyrolyzed in a vacuum reactor with high temperature (900 degrees C) and long contact time (more than 2 h). Beneficial synergetic effect on gas yield was clearly observed. Gas yield of blend fuel was evidently higher than that of both parent fuels. The gas volume yield, gas lower heating value (LHV), fixed carbon conversion and H-2/CO ratio were 1.42 Nm(3)/kg((blend fuel)), 10.57 MJ/Nm(3), 96.64% and 0.88% respectively, which indicated this new method a feasible one for gas production. It was possible that sewage sludge acted as gasification agents (CO2 and H2O) and catalyst (alkali and alkaline earth metals) provider during co-pyrolysis, promoting CO2-char and H2O-char gasification which, as a result, invited the improvement of gas volume yield, gas lower heating value and fixed carbon conversion. (C) 2014 Elsevier Ltd. All rights reserved.