The physicochemical properties of pyocin F1 were studied. Pyocin F1 consists of flexuous rod-like particles homogeneous in size. Each particle was composed of rod and fiber parts. The rod part was 105.5±9.5nm long and 10.0±1.4nm wide, and showed regular striations amounting to 23 layers. The fiber part was composed of several filaments; the length of the longest filament was 43.0±12.0nm. The amino acid composition, the partial specific volume (0.720ml/g), the sedimentation coefficient (s⁰_{20, W}=35.1S), and the translational diffusion constant (0.94±0.01×10^-7cm²/s) were determined. The particle weight was calculated to be 3.23×10⁶ daltons.