Microalgae are very promising in biodiesel production. To reduce the production cost, approaches to enhance lipid and triacylglycerols (TAGs) production by microalgae have gained much attention. Effect of ethyl-2-methyl acetoacetate (EMA) on the lipid and TAGs production by a freshwater microalga, Scenedesmus sp. LX1, was studied in this paper. EMA below a concentration of 2 mg L(-1) had no significant effect on microalgal biomass or lipid production. The biomass and lipid productivity were about 0.47 g L(-1) and 139 mg L(-1), respectively, and the lipid content per biomass was about 30% (w/w). Promisingly, comparing with the one without EMA treatment, under EMA concentrations of 1.0-2.0 mg L(-1) the TAGs content per lipid (about 20% (w/w)) and TAGs productivity (about 23 mg L(-1)) were increased by 79% and 40%, respectively. Therefore, exposing algal cells with trace amount of EMA offers a viable method to enhance the TAGs production in Scenedesmus sp. LX1. (c) 2010 Elsevier Ltd. All rights reserved.