Abstract: Disclosed is an antibacterial nanofiber which comprises a polymer having an electron-withdrawing group and/or an electron-withdrawing atomic group and has an average fiber diameter of not less than 1 nm and less than 1000 nm, wherein the ratio of the binding energy of the minimum unit of the polymer at 25° C. to the binding energy of the electron-withdrawing group and/or the electron-withdrawing atomic group contained in the minimum unit of the polymer at 25° C. is 0.13 or greater. The nanofiber has an antibacterial activity by itself, and therefore can exhibit an antibacterial activity without the need of adding any antibacterial agent.