Magnetotactic bacteria have one or more chains of magnetosome, consisting of nano-sized magnetic crystal covered with a phospholipid bilayer and use it to sense the geomagnetic fields. In order to elucidate the molecular process to make magnetosome from the iron compounds found in the bacteria, laser Raman spectroscopic measurements were performed with the magnetotactic bacterium, Magnetospirillum magnetotacticum MS-1 and the fractions separated from it. The major Raman signals at 662 cm⁻¹ and 740 cm⁻¹ were observed. The former was assigned to the Raman signal of magnetite and the latter, to that of ferrihydrite. The Raman signal of ferrihydrite was observed not only in the membrane fraction, but also in the cytoplasmic fraction. Based on the results, the role of ferrihydrite in magnetosome synthesis in the magnetotactic bacteria was discussed.