Rice hull hydrolysate was used as feedstock for microbial lipids production using the oleaginous fungus Mortierella isabellina. Kinetic experiments were conducted in C/N ratios 35, 44 and 57 and the oil accumulation into fungal biomass was 36%, 51.2% and 64.3%, respectively. A detailed mathematical model was used in order to describe the lipid accumulation process. This model was able to predict reducing sugar and nitrogen consumption, fat-free biomass synthesis and lipid accumulation. Neutral lipids constitute the predominant lipid fraction, while the major fatty acids were oleic, palmitic and linoleic acid. Fatty acids of long aliphatic chain were not detected, thus the microbial oil produced is a promising feedstock for biodiesel production. (C) 2011 Elsevier Ltd. All rights reserved.