This study focused on the effects of the use of hydrous ethanol with high water contents up to 40% on the performance and emissions of a small spark ignition engine for a generator. The effects of loads and ethanol water contents on engine performance and emissions were investigated. The results show that for ethanol with 5% water content (Eh95) at constant engine speed of 3600 rpm and at stoichiometric air-fuel ratio, CO and HC + NOx emissions after the catalytic converter were lower than the EPA limit model year 2011 tested under same load conditions of California exhaust emission standards and test procedures for 2005 and later small off-road engines. However for emissions before the catalytic converter, only CO is lower than the EPA limit model year 2011, while HC + NOx is higher. Increasing loads increased the overall efficiency, while BSFC, HC, formaldehyde and acetaldehyde emissions decreased. Increasing water content at constant load decreased overall efficiency and NOx emission, while BSFC, HC, CO, formaldehyde and acetaldehyde emissions were increased. A catalytic converter is required to reduce the regulated and unregulated emissions when hydrous ethanol is used for a small SI engine generator set. (C) 2012 Elsevier Ltd. All rights reserved.