In present study, repeated-batch fermentation in biofilm reactor was evaluated for ethanol production by using carob extract. Response surface method (RSM) was used to determine optimum initial sugar concentration, pH, and agitation in the constructed biofilm reactor. The optimum conditions for ethanol production in biofilm reactor were determined as initial sugar content of 7.71 degrees Bx, pH of 5.18 and agitation of 120 rpm. The ethanol production (P), the yield (Y-P/S) and production rate (Q(P)) were found as 24.51 g/L 48.59% and 2.14 g/L/h at the optimized conditions, respectively. The fermentation time for maximum ethanol production in carob extract was reduced to 12 h by using a biofilm reactor compared the published data in the literature, which was 30 and 24 h by using suspended and immobilized yeasts in a stirred tank reactor, respectively. Furthermore, the effect of various nitrogen sources and enrichment were also evaluated and Y-P/S, Q(S) and Q(P) were significantly decreased compared to the results obtained from optimum conditions in biofilm reactor. Overall, results showed that a biofilm reactor for ethanol production from carob extract can be successfully implemented in point of reducing fermentation time, eliminate re-inoculation of the typical batch fermentation as well as increasing production yield. (C) 2015 Elsevier Ltd. All rights reserved.