To enhance the thermal stability of poly(vinvl alcohol) (PVA) fiber, the fiber was prepared from the g l spinning of high molecular weight (HMW) PVA by using dimethyl sulfoxide/water (8/2, v/v) as a solvent, accompanied with the cross-link by boric acid (B-PVA). In addition, the structure and properties of the B-PVA fiber were compared with those of the HMW PVA fiber obtained by using the same spinning system without cross-linking (NB-PVA). Through a series of experiments, it turned out that cross-linking actualized by an optimum amount of boric acid (0.3 wt % based oil PVA) and zone drawing caused significant changes in the properties of HMW PVA gel fiber. That is, cross-linking increased thermal degradation temperatures at each degradation step and amounts of final residues, resulting in improving thermal properties of the PVA fiber. On the contrary, it was found that in the case of the B-PVA fiber, some broadening of the original PVA unit cell occurred, which was identified by the peak shift to lower angle in X-ray diffractogram. The tensile strength and Young's modulus of B-PVA fiber with draw ratio of 15 are 23.1. and 308.3 g/d, respectively. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 1733-17-38, 2009