An isotactic polypropylene hollow microfiber was continuously produced by using a carbon dioxide (CO2) laser-thinning method. To prepare the hollow microfiber continuously, the apparatus used for the thinning of the solid fiber was improved so that the laser can circularly irradiate to the hollow fiber. Original hollow fiber with an outside diameter (OD) of 450 pm and an internal diameter (ID) of 250 mu m was spun by using a melt spinning machine with a specially designed spinneret to produce the hollow fiber. An as-spun hollow fiber was laser-heated under various conditions, and the OD and the ID decreased with increasing the winding speed. For example, when the hollow microfiber obtained by irradiating the CO2 laser to the original hollow fiber supplied at 0.30 m min(-1) was wound up at 800 m min(-1), the obtained hollow microfiber had an OD of 6.3 mu m and an ID of 2.2 mu m. The draw ratio calculated from the supplying and the winding speeds was 2667-fold. The hollow microfibers obtained under various conditions had the hollowness in the range of 20-30%. The wide-angle X-ray diffraction patterns of the hollow microfibers showed the existence of the highly oriented crystallites. Further, the OD and ID decreased, and the hollowness increased by drawing hollow microfiber obtained with the laser-thinning. (c) 2006 Wiley Periodicals, Inc.