We succeeded in producing nylon 6 microfibers with a continuous-thinning method with a carbon dioxide (CO2) laser. A laser-thinning apparatus used to continuously prepare microfibers was developed in our laboratory; it consisted of spools supplying and winding the fibers, a continuous-wave CO2-laser emitter, a system supplying the fibers, and a traverse. The laser-thinning apparatus produced microfibers in the range of 100-2500 m min(-1). The diameter of the microfibers decreased as the winding speed increased, and the birefringence increased as the winding speed increased. When microfibers, obtained through the laser irradiation (at a power density of 19.8 W cm(-2)) of the original fiber supplied at 0.32 m min(-1), were wound at 848 m min(-1), they had a diameter of 3.2 mum and a birefringence of 47 x 10(-3). The draw ratio calculated from the supplying and winding speeds was 2650x. Scanning electron microscopy showed that the microfibers obtained with the laser-thinning apparatus had smooth surfaces not roughened by laser ablation that were uniform in diameter. Wide-angle X-ray diffraction photographs of the microfibers wound at 566 and 848 m min(-1) showed equatorial and meridional reflections due to the gamma from. These reflections gradually became clear as the winding speed increased. The developed apparatus more easily produced microfibers than conventional technologies, such as conjugate spinning, islands-in-a-sea fiber spinning, melt blowing, and flash spinning. (C) 2004 Wiley Periodicals, Inc.