AbstractA study was carried out on the wet spinning of chitosan fibers using 2% acetic acid as a solvent, 10% aqueous sodium hydroxide as a nonsolvent, and 4% chitosan solution as a polymer concentration. In this study, we investigated the effect of the ripening time of the spinning dope on the ability of fiber formation (i‐value), structure, thermal, and mechanical properties (such as fineness, tenacity, elongation, work of rupture, etc.) of chitosan fibers. Based on the results, it can be seen that the ripening time of spinning dope (in days), with the same polymer concentration of spinning dope, changes from 1 to 8, and the i‐value of the spinning dope increased with an increasing of the ripening time. At the ripening time of 8 days, tensile strength, elongation, and work of rupture showed minimum value attributed to the excessive degradation of the chitosan polymer chains left from the mixing operation that took place at the same time as the ripening time of the spinning dope, which means that the optimum ripening time of the spinning dope is 1 to 7 days. However, the thermal decomposition temperature and the onset of the exothermic temperature of thermal properties decreased with an increased ripening time. On the other hand, tenacity, elongation, and toughness decreased with increasing ripening time, and these qualities radically decreased with an increasing ripening time of more than a week. This indicates that the dispersion of aggregates and the degradation of chitosan polymer chains left from the mixing operation occurred at the same time during the ripening time of the spinning dope. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2870–2877, 2003