Abstract: Polyethylene naphthalate fibers that are characterized in that the fibers have a crystal volume of from 550 to 1,200 nm3 obtained by wide angle X-ray diffraction of the fiber and a degree of crystallization of from 30 to 60%. It is preferred that the fibers have a maximum peak diffraction angle of wide angle X-ray diffraction of from 25.5 to 27.0° and a melting point of from 285 to 315° C. The production method thereof is characterized in that a particular phosphorus compound is added to the polymer in a molten state, the spinning draft ratio after discharging from the spinneret is from 100 to 5,000, and the molten polymer immediately after discharging from the spinneret is allowed to pass through a heat-retaining spinning chimney at a temperature within ±50° C. of a temperature of the molten polymer, and is drawn.