In this study, we investigated the sintering characteristics of incinerator residues that were obtained from sewage sludge by heating the residues from 1000 to 1100 °C for 30 min. The bulk density of the sintered monoliths, ranging from 0.6 to 1.0, decreased significantly when the sintering temperature increased from 1050 to 1100 °C. The major crystalline phases identified in the raw ash were quartz (SiO2), hematite (Fe2O3), Al2O3, and AlPO4; small amounts of Na2O and K2O were also detected. Higher sintering temperatures, 1050 and 1100 °C, resulted in porosities of 33 and 43 %, respectively, but variations were profound, because both the pore volume and the pellet volume increased concurrently. The amount of quartz decreased on sintering, with the intensity of the major peak decreasing further as the sintering temperature increased. SEM images confirmed the presence of SSA aggregates treated at 1100 °C; spaces existed between the sintered SSA particles, due to the formation of larger pores by excessive bloating. Moreover, the targeted heavy metal leaching concentrations in the sludge ash samples all met the current regulatory thresholds of the Taiwan Environmental Protection Agency.