A semi-solid fermentation process for the production of biodiesel from sweet sorghum is introduced. The microorganism used is the oleaginous fungus Mortierella isabellina, which is able to transform efficiently sugar to storage lipid. Kinetic experiments were performed at various water content percentages. The fungus consumed simultaneously sugars and nitrogen contained in sorghum and after nitrogen depletion the biomass growth was completed and oil accumulation began. Water content of 92% presented the highest oil efficiency of 11 g/100 g dry weight of substrate. The semi-solid process is shown to have certain advantages compared to liquid Cultures or solid-state fermentation and gives oil of high quality. (C) 2009 Elsevier Ltd. All rights reserved.