Conductive carbon felts (Cf) were used as biofilm carriers in bioelectrochemical reactors to enhance the electrical stimulation on treatment of phenol-containing synthetic wastewater. In batch test, phenol biodegradation was accelerated under an optimum direct current (DC), which was 2 mA for Cf biofilm carriers, lower than that for non-conductive white foam carriers. The stimulation effect was consistent with Adenosine Triphosphate contents in biofilms. The long-term operation further demonstrated that a high and stable phenol removal efficiency could be achieved with applied DC of 2 mA, and intermittent DC application was better than continuous one, with phenol removal efficiency of over 97%. Although the quantities of whole microbial communities kept at a high level under all conditions, special microorganisms related with genera of Zoogloea and Desulfovibrio were distinctively enriched under intermittent applied DC pattern. This study shows that the electrical stimulation is potentially effective for biofilm reactors treating phenol-containing wastewater. (C) 2015 Elsevier Ltd. All rights reserved.