Biodiesel, a promising alternative fuel, is not a completely renewable fuel, as it currently uses oil-based methanol for its industrial production. Integrated biodiesel and bioethanol production in a biorefinery unit can overcome this challenge together with an improved economy. In this study, castor plant was applied to an integrated biodiesel and ethanol production. The extracted oil was transesterified with ethanol produced through simultaneous saccharification and fermentation of the castor plant residue. An alkaline pretreatment using 8% w/v sodium hydroxide at 100 degrees C for 60 min was applied to improve the ethanol production yield from 27.2 to 71.0%. An experimental design using response surface methodology (RSM) was used to optimize the biodiesel production yield. The optimum biodiesel yield was 85.0 +/- 1.0%, obtained at 62.5 degrees C using an ethanol to oil mass ratio of 0.29:1 for 3.46 h, which was in agreement with the predicted yield (84.4%). Accordingly, 1 kg of castor plant resulted in production of 149.6 g biodiesel and at least 30.1 g ethanol as the final products with no extra alcohol feedstock requirement. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.