The morphology and composition of living diatoms were explored at different heating rates, in which the marine diatom Navicula sp. was selected as experimental materials. First, the frustules from living diatoms were cleaned by hydrochloric acid to remove metal oxide and other inorganic salts. After that, chemically purified frustules were heated to 600 ℃ at the heating rates of 1 ℃/min, 3 ℃/min, 5 ℃/min and 7 ℃/min for 2 h. The morphology and composition of diatom frustules at different stages were characterized by Fourier Transform Infrared Spectra (FTIR), Scanning Electronic Microscopy (SEM), and Energy Dispersive X-ray Analysis (EDS). Obtained results show that the SiO2 contents increase with the slowdown of the heating rate. The highest SiO2 content in the diatom frustules is obtained when they are baked at 600℃ at a heating rate of 1℃/min for 2 h, reached about 90%, and they will maintain a shape perfectly with few impurities. These results mean that organic matter is difficult to be removed with a fast heating speed because the biosilica structures of frustules are characterized by good thermal insulator and slower heat transfer. Moreover, higher temperatures and longer maintaining temperature will effect the morphology of diatom frustules. Therefore, it suggests that the slower heating rate is beneficial to removing organic matters and ensuring the integrity of diatom appearance.