Poly(vinyl alcohol) (PVA) is an important water‐soluble polymer. In this study, a novel method has been developed for preparing water‐soluble PVA fiber with narrowly dissolving temperature range via wet spinning of partly acetalized PVA. The structures and properties of the fiber were characterized by IR, 1H‐NMR, DSC, WAXD, tensile strength tester, etc. IR and NMR spectra showed that acetal groups were successfully generated on the lateral chains of PVA with the catalysis of acid. As a small quantity of CH2O was added, the introduction of the acetal group could reduce both the hydrophilicity of amorphous region and the crystallinity of PVA water‐soluble fiber, and hence narrowed the dissolving temperature range of fiber. However, the dissolving temperature range was broadened with a further increase of CH2O amount, because of the large decrease of crystallinity and crystallite perfection. When the CH2O added amount reached up to 20%, the acetalized PVA was completely insoluble, so that the spinning process could not be carried out. The breaking strengths of most acetalized fibers were beyond 4 cN/dtex, which satisfied the ordinary use of industrial and domestic field. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012