The characteristic rheological responses of solutions of atactic poly(vinyl alcohol) (PVA) in dimethyl sulfoxide were investigated in terms of the concentration and molecular weight. The syndiotactic dyad content and weight-average molecular weight of PVA were 52% and 85,000-186,000, respectively. On a modified Cole-Cole plot, the solutions did not give a single master curve with a slope of 2 but gave various curves with slopes of less than 2. Furthermore, the slope slightly decreased with increasing concentration. The deviation from the master curve indicated that the solutions were rheologically heterogeneous, despite optical transparency. Among the PVA solutions, the 14 wt % solutions exhibited very unusual rheological behavior. The loss tangent changed with the shear rate and produced three distinct regions, which indicated a shear-induced phase transition. With respect to Winter's view on gelation, the 14 wt % solutions underwent a double sol-gel transition as the shear rate increased over the frequency range of 0.05-500 rad/s. However, the molecular weight did not have such noticeable effects on the rheological behavior over the concentration range of 10-14 wt %. (C) 2004 Wiley Periodicals, Inc.