The effect of mature compost (MC) used as a bulking agent on ammonia, hydrogen sulfide, and short-chain fatty acids emission reduction during sewage sludge (SS) composting process was studied in this paper. Three types of mixtures, single SS, SS þ wood chips (SS þ WC), and SS þ MC, were composted in a laboratory reactor. Among the different treatments, decrement rates of NH 3 emission (based on initial TN) from SS to SS þ MC and SS þ WC to SS þ MC were 63 and 59%, respectively. The H 2 S concentration ranged from 0.759 to 1.140 mg m À3 for SS, from 0.075 to 0.455 mg m À3 for SS þ WC, and from 0.075 to 0.425 mg m À3 for SS þ MC and the short-chain fatty acids (C 2 -C 5 ) concentration ranged from 0.10 to 1.00 ppm for SS, from 0.10 to 1.50 ppm for SS þ WC, and from 0.10 to 0.80 ppm for SS þ MC. In addition, the temperature apparently, as well as the thermophilic stage, was also elevated by bulking agent addition, especially by the MC addition. The denaturing gradient gel electrophoresis analysis indicated that there was more diversity of the bacterial community during the SS þ MC process. According to these results, MC was a suitable bulking agent for reduction ammonia, hydrogen sulfide, and short-chain fatty acids emission during the SS composting.