Nlon 6 fibers were zone drawn and zone annealed by using a continuous wave carbon dioxide laser to develop their mechanical properties. A laser-heating zone drawing was carried out under a applied tension of 35.4 MPa at a power density of 9.65 W . cm(-2), and then the zone-drawn fiber was annealed. A laser-heating zone annealing was carried out in two steps at a power density of 9.65 W . cm(-2); the first step was carried out under 423 MPa and the second under 517 MPa. The treating temperature of the fiber heated by the CO2 laser was measured by using an infrared thermographic camera equipped with a magnifying lens. The treating temperature at the zone drawing is 138 degreesC, and those at the first and the second zone annealing are 121 and 125 degreesC, respectively. The second laser-heated zone-annealed fiber has a birefringence of 65.2 x 10(-3), a degree of crystallinity of 54%, and a storage modulus of 21 GPa at 25 degreesC. Wide-angle X-ray diffraction patterns for the laser-heated zone-drawn and the zone-annealed fibers show (200) reflection and (002/202) doublet due to only an alpha form on the equator. The laser-heated zone-drawn fiber has a melting endotherm peaking at 216 degreesC and a trace of shoulder on the higher temperature side of its peak, and the laser-heated zone-annealed fibers have a single melting endotherm peaking at 216 degreesC.