An isotactic polypropylene (i-PP) microfiber was obtained by irradiating a carbon dioxide laser to previously drawn fibers. To prepare the thinner i-PP microfiber, it is necessary to previously draw original i-PP fibers under an applied tension of 7.8 MPa at a drawing temperature of 140degreesC. The drawn fiber was heated under an applied tension of 0.3 MPa using the laser operated at a power density of 39.6 W cm(-2). The thinnest i-PP microfiber obtained under optimum conditions had a diameter of 1.8 mum and a birefringence of 30 x 10(-3). Its draw ratio estimated from the diameter reached 51,630. It is so far impossible to achieve such a high draw ratio by any drawing. The wide-angle X-ray diffraction photograph of the microfiber shows the existence of the oriented crystallites. Laser-heating allows easier fabrication of microfibers compared with the conventional technology such as the conjugate spinning. (C) 2004 Wiley Periodicals, Inc.