Activated sludge with its high lipid content is a potential raw material for producing biodiesel. Sub-critical water (SCW) treatment has been known to be a cheap and effective method for reducing organic compounds, especially carcinogenic aromatic compounds such as polycyclic aromatic hydrocarbons or polychlorobiphenyls in activated sludge as well as increasing the amount of extractable lipids. In this work, the amount of neutral lipids and fatty acid profiles in neutral lipids extracted from activated sludge both with and without SCW pre-treatment were investigated. Results showed that the amount of neutral lipid extracted from SCW treated activated sludge is almost four times to those without SCW treatment. However, there is no observable difference between the fatty acid profiles of neutral lipids obtained from activated sludge with and without SCW treatment. At least 14 kinds of fatty acids were identified in the neutral lipids of sludge oil. (C) 2010 Elsevier Ltd. All rights reserved.