Dynamic compositions of lipids accumulated in two diatoms Chaetoceros gracilis and Nitzschia closterium cultured with nitrogen and silicon deprivation were studied. It was found that short-chain fatty acids (C-14-C-16) content was much higher than long-chain fatty acids (C-18-C-20) content in lipids of two diatoms. The pyrolytic characteristics of biodiesel made from two diatoms and two plant seeds were compared by thermogravimetric analysis. The highest activation energy of 46.68 kJ mol(-1) and the minimum solid residue of 25.18% were obtained in the pyrolysis of biodiesel made from C. gracilis cells, which were cultured with 0.5 mmol L-1 of nitrogen (no silicon) and accumulated the minimum polyunsaturated fatty acid (C-20:5). The pyrolysis residue percentage of C gracilis biodiesel was lower than that of N. closterium biodiesel and higher than those of plant (Cormus wilsoniana and Pistacia chinensis) biodiesels. (C) 2014, The Society for Biotechnology, Japan. All rights reserved.