Time-resolved light scattering measurements were performed on gelation processes of poly(vinyl alcohol) (PVA) solutions at 25 degrees C in mixtures of dimethyl sulfoxide (DMSO) and water (H2O) with volume ratios of 60/40 and 80/20. It was found that the scattering profile I(Q) from a 60/40 (DMSO/H2O) solution has a maximum whose position Q(m) is independent of time and that the intensity I(Q) at Q = Q(m) increases exponentially with time. These observations agree with the theoretical predictions for the initial stage of spinodal decomposition (SD) type phase separation, while the scattering profile I(Q) from a 80/ 20 solution has no peak. It is therefore concluded that the SD type microphase separation occurs before gelation in the 60/40 solution, but not in the 80/20 solution. On the basis of present, as well as past results, a possible mechanism of the gelation process for PVA solutions has been proposed.