Ethanol-type sludge fermentation has recently attracted much attention because it can en-hance direct interspecies electron transfer and thus improve the anaerobic digestion of waste activated sludge (WAS).In this paper,the enhancement of short-term ethanol-type fermentation of WAS via adding Saccharomyces was investigated.The experimental results show that the maximum ethanol production of 1030.8 ± 20.6 mg/L was achieved,with the optimum fermentation conditions of a pH of 5.1,temperature of 26.0 ℃ and time of 8.0 hr.Although the content of volatile fatty acid (VFA) increased within 10 hr,it is one order of magnitude lower than the content of ethanol,indicating that the VFA generation did not affect the efficient production of ethanol.The analyses of changes in the microbial commu-nity during the fermentation process demonstrate that the greatest Saccharomyces activity occurred in the first 8 hr and it can play an important role in ethanol production even at a very low relative abundance.Meanwhile,most typical acid-producing bacteria were inhib-ited,but the hydrogenotrophic methanogens (i.e.,Methanobacterium) were enriched to a cer-tain extent.Further statistical analyses reveal that the Rhodobacter,Thermomonas,Terrimonas and Saecharomyces are responsible for ethanol production during the fermentation.However,these findings not only provide a reference for the development of enhancing ethanol-type fermentation of sludge,but also are expected to provide a new way of thinking for the effi-cient bioenergy and resource recovery from sludge.