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The properties of molded products are strongly affected by the molecular orientation induced by flows in the molding process. To improve the quality of the final product and reduce production costs, it is necessary to understand how the flows affect both the direction and degree of orientation of polymers. Thus, many experimental and numerical studies have reported the flow-induced orientation and structure of polymeric liquids. In most experimental studies, optical measurements such as small angle scattering or flowinduced birefringence (FIB) have been used to examine the flow-induced orientation of the polymers. Flows around obstacles and contraction flows have attracted the interest of researchers who study complex flow fields. In the case of flows around obstacles, Yasuda et al. measured the FIB of flows in a polymer solution around a tiny cylinder and found that the molecular orientation of the polymer was dramatically changed in the region upstream of the cylinder. They also reported that the higher-orientation state was sustained along the centerline in the downstream region. Mitsoulis numerically analyzed birefringence patterns in flows of polymer melts around a cylinder. In the case of contraction flows where the viscoelastic properties of the fluid are strongly affected, Quinzani et al. measured the distribution of birefringence in a viscoelastic planar flow with an abrupt contraction, using the FIB technique and analyzing the stress fields. Azaiez et al. and Favero et al. numerically analyzed velocity profiles, shear stresses, and normal stress differences in a viscoelastic planar abrupt contraction flow. They showed that their results qualitatively matched the experimental data obtained by Quinzani et al.. Martyn et al. investigated the relation between the birefringence and stress fields in a viscoelastic melt flow in a planar abrupt contraction channel. Flows with abrupt expansions in thin dies commonly occur in polymer processing. Although the channel geometry is symmetric with contraction flow, the flow is expected to be more complex because the flow structure of the polymer is expected to be affected by the upstream flow conditions. Effect of Cross-Sectional Aspect Ratio on Flow-Induced Orientation of a Polymer Solution in Planar Channels with an Abrupt Expansion