Poly(ethylene-2,6-naphthalate) (PEN) nanofiber was prepared by a carbon dioxide (CO2) laser supersonic drawing. The CO, laser supersonic drawing was carried out by irradiating the laser to the as-spun) PEN fiber in a low-temperature supersonic jet. The supersonic jet was generated by blowing off air into a vacuum chamber from a fiber supplying orifice. The flow velocity from the orifice can be estimated by applying Graham's theorem from the pressure difference between the atmospheric pressure and the pressure of the vacuum chamber. The fastest flow velocity estimated was 396 m s(-1) (Mach 1.15) at a chamber pressure of 6 KPa. The nanofiber obtained at Mach 1.15 was the oriented nanofibers with an average diameter of 0.259 mu m, and its draw ratio estimated from the diameters before and after the drawing reached 430,822 times. The CO2 laser supersonic drawing is a new method to make nanofiber without using any solvent or removing the second component. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1913-1919, 2010