The electroviscosities of solutions of a lyotropic liquid crystalline polymer, poly(n-hexyl isocyanate), were investigated by a slit viscometer. The morphologies of the solutions being studied include the isotropic, the biphasic, and the fully liquid crystalline. All three morphologies exhibit viscosity enhancements with imposition of an electric field. However, the electrorheological behavior of the isotropic solution is different from those of other morphologies. The isotropic solution starts with a higher field free viscosity and its electroviscosity increases gradually with the increasing electric field strength. In contrast, the anisotropic solutions begin with lower zero field viscosities and the electroviscosities increase sluggishly until a critical field strength is reached; the viscosities then increase rapidly and finally exceed that of the isotropic solution. For the morphologies of the biphasic and the fully liquid crystalline, the dependence of the viscosity enhancements on field strength and shear rate can be described by a single variable. The variable scales with the square of the electric field strength and the reciprocal of the shear rate. By introducing the effect of the molecular permanent dipole moments into Doi’s theory, the electrorheological effects of PHIC solutions can be satisfactorily interpreted.