Aims: To study and characterize the lipids produced by Mortierella (Umbelopsis) isabellina, during its growth on mixtures of glucose and xylose. Methods and Results: Glucose and xylose were utilized as carbon sources, solely or in blends, under nitrogen-limited conditions, in batch-flask trials (initial sugars at 80 g l(-1)). Significant lipid production (maximum lipid 17.8 g l(-1); lipid in DCW 61.0% w/w; lipid on glucose consumed 0.23 g g(-1)) occurred on glucose employed solely, while xylose concentration in the growth medium was conversely correlated with lipid accumulation. With increasing xylose concentrations into the blend, lipid storage decreased while xylitol in significant concentrations (up to 24 g l(-1)) was produced. Irrespective of the sugar blend employed, significant quantities of endopolysaccharides were detected in the first growth steps (in the presence of nitrogen into the medium or barely after its disappearance) while lipids were stored thereafter. Neutral lipids, mainly composed of triacylglycerols, were the main microbial lipid fraction. Phospholipids were quantified both through fractionation and subsequent gravimetric determination and also through determination of phosphorus, and it seemed that the second method was more accurate. Phospholipids were mainly composed of phosphatidylcholine and another nonidentified compound presumably being phosphatidyldimethylethanolamine. Conclusions: Mortierella isabellina is suitable to convert lignocellulosic sugars into lipids. Significance and Impact of the Study: Differentiations between metabolism on xylose and glucose were reported. Moreover, this is one of the first reports indicating extensive analysis of microbial lipids produced by M. isabellina.