To examine the processability of four commercial grades of the domestic polystyrenes (GP125, GP/150, HI425 and HI425E) in the vicinity of the actual processing conditions, the steady shear flow properties such as viscosity (η), first normal stress difference (N_l) and second normal stress difference (N₂) were measured by use of a capillary type instrument. And the dynamic properties were investigated by a parallel plate type instrument. All grades of polystyrenes showed a non-Newtonian flow properties over the range of shear rates investigated. In general, high impact (HI) grades showed slightly higher melt viscosities than general purpose (GP) grades. The viscosity data also suggested that the use of the melt index as a parameter for the polymer fluidity gave us an errorneous conclusion to evaluate the actual polymer processing. An inspection of N_l and N₂ revealed that GP grades showed higher melt elasticity than HI grades, and the ratio of -N₂/N_l lay between 0.14 and 0.72 for the four grades of polystyrenes tested. Comparison of capillary rheometer data with the dynamic data yielded a close analogy That is, the shapes of viscosity curves and the dynamic viscosity curves were similar and in the same range. However, the shapes of N₁ curves and the dynamic storage modulus curves showed some discrepancy at the high range of shear rates of frequencies, due probably to different deformation history and mode between steady shear and dynamic flows.