In this work, microbial conversion of wastewater from butanol fermentation to microbial oil by oleaginous yeast Trichosporon dermatis was carried out for the first time. Wastewater with high COD generated from butanol fermentation mainly contained acetic acid, butyric acid and residual sugars (xylose and arabinose). Without any pretreatment and adding nutrients (nitrogen sources and trace elements), this wastewater was utilized by oleaginous yeast T. dermatis for microbial oil production. After five days' fermentation, the COD of this wastewater has been removed for about 68%, and the highest biomass and lipid content of T. dermatis were 7.4 g/l and 13.5% respectively. This bioconversion could both solve the environmental problem and offer low-cost lipid feedstock for biodiesel production. (C) 2012 Elsevier Ltd. All rights reserved.