Nylon 46 fibers produced by the high-temperature zone-drawing treatment were treated by repeating high-tension annealing treatments, that is, a high-tension multiannealing (HTMA) treatment to improve their tensile properties. The HTMA treatment was carried out at a repetition time of 10 times and treating temperature of 110 degrees C under high tension (538.2 MPa) close to the tensile strength at break. Although the HTMA treatment was carried out at 110 degrees C, which is much lower than the crystallization temperature of 265 degrees C for nylon 46, the degree of crystallinity increased up to 59%. The orientation factor of crystallites increased dramatically up to 0.949 by the first high-temperature zone-drawing treatment and slightly during the subsequent treatments. This observation indicated that the orientation of crystallites due to slippage among molecular chains did not occur during the HTMA treatment. The treatments shifted the melting peak to slightly higher temperatures, and the HTMA fiber has a melting endotherm peaking at 285 degrees C. The fiber obtained finally had a storage modulus of 12.5 GPa at 25 degrees C.