As can be observed in pearls, corals and shells, organisms synthesize inorganic substances of a fine structure and outstanding physical properties, which cannot be imitated artificially. This formation of inorganic substances in organisms is called biomineralization, in particular. In vivo organic molecules play an important role in biomineralization, and inorganic substances are formed under a mild condition. Therefore, biomineralization has attracted much attention in the area of functional material development as the inorganic material synthesis process with a low environmental loading. With a focus on magnetic particulates synthesized by magnetotactic bacteria, our laboratory is conducting the research to clarify biomineralization mechanism and the development of functional bionanomaterials using this mechanism.