The phase separation of poly(vinyl alcohol) (PVA) in dimethyl sulfoxide/water mixtures was investigated by using light scattering techniques in terms of the degree of polymerization and stereo-regularity. Atactic (at-) and syndiotactic (st-) PVA, the degrees of polymerization (P) being 17 900 and 1980, respectively, were used as test specimens. The analysis was mainly performed in comparison with previous results obtained for at-PVA (P = 2000) whose degree of polymerization is similar to that (P = 1980) of st-PVA, but lower than that (P = 17 900) of at-PVA used in the present work. The phase separation occurred rapidly when the content of dimethyl sulfoxide in the mixed solvent was 50-70 vol%. This tendency was found to be significant for st-PVA with high stereo-regularity, but to be almost independent of the degree of polymerization of at-PVA. The logarithm of scattered intensity from at-and st-PVA solutions increased linearly with time in the initial stage of the phase separation. If this phenomenon could be analysed within the framework of the linear theory of spinodal decomposition proposed by Cahn (J. Chem. Phys., 1965, 42, 93) the phase diagram of st-PVA was classified into four regions : (I) a homogeneous sol region, (II) a sol region under spinodal temperature, indicating only spinodal decomposition, (III) a gel region under the spinodal curve, indicating simultaneous advance of both gelation and spinodal decomposition, and (TV) a gel region above the spinodal line, independent of liquid-liquid separation. On the other hand, for at-PVA, region II could not be observed and region IV existed only in a very narrow temperature range, which is similar to the result observed for at-PVA (P = 2000) solutions in previous work. The drawability of the dried gel film was affected by the composition of the solvent mixture and by quenching temperature of the solutions, but it was hardly affected by the stereo-regularity. This interesting phenomenon is discussed in terms of morphology of gels and films, as studied by crystallinity, X-ray diffraction, birefringence and small angle light scattering under Hv polarization condition. As the results show, it turned out that the greatest significant drawability is related to a continuous tissue with honeycomb-like structure associated with rapid phase separation of PVA solutions due to thermodynamic instability.