The constant rotational rheological behaviors of PAN/DMSO solutions with two kinds of nonsolvent (water and ethanol) have been investigated, respectively, using a cone-plate rheometer. From viscosity measurements, the flow behavior was described within the shear rate range 0.1-1000 s(-1). The PAN solutions show shear thinning at high shear rates. The viscosities of the solutions decreased with the rising of the temperature at low shear rate. H2O content has great influence on the viscosity of the solutions, depending on the hydration of H2O and PAN or desolvent effect, according to different H2O content. The role of ethanol compared with H2O was also researched and higher viscosity was found. Non-Newtonian index, structural viscosity index Delta eta, and flow activation energy of the PAN/DMSO/H2O systems were also studied. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 598-602, 2009