The bacterial flagellum consists of at least three substructures: basal body, hook, and filament. The basal body is embedded in the cytoplasmic membrane and consists of a rod with an inner ring (MS ring) and two outer rings (L and P rings). The rod is the transmission shaft between the flagellar rotary motor and the hook, and consists of four proteins: FlgB, FlgC, FlgF, and FlgG. We have worked out purification of these four rod proteins from Salmonella typhimurium overproduced in E. coli and have been trying to characterize their assembly behaviors and intermolecular interactions. We are also planning to do structure analysis of the rod by X-ray crystallography and electron cryomicroscopy.