Vermifiltration is an alternative and low-cost technology for stabilizing excess sludge from domestic wastewater treatment plants. The biofilm properties of a vermifilter (VF) with earthworms, Eisenia fetida, for domestic wastewater sludge (DWS) treatment were studied. A biofilter (BF) without earthworms served as the control. VF biofilms had lower levels of suspended solids (SSs), volatile SS, C, H, N and S contents, protein-like groups, and total viable cell numbers and larger humic acid-like fractions and protease, dehydrogenase, lipase, and amylase activities compared with BF biofilms. Furthermore, VF biofilms featured richer diversity in their microbial community and more populations of Proteobacteria than BF biofilms. The relationships between organic matter and microbial eco-physiological indices in VF biofilms were significantly different from those in BF biofilms. Overall findings indicated that earthworm presence remarkably decreases organic matter contents and microbial biomass and improves microbial enzyme activities and the community structure of VF biofilms. (C) 2013 Elsevier B.V. All rights reserved.