The electrorheological (ER) effect of an anisotropic solution of poly(gamma-benzyl-L-glutamate) (PBLG) in 1,4-dioxane with a concentration of 15 wt % was measured at a shear rate of 2.6 s(-1) by our parallel-plate sliding rheometer. The solution under shear flow was stimulated by stepwise electric fields up to 3.0 kV/mm. Remarkable changes in the beginning of the transient ER response were observed according to the strength of the stepwise electric fields. The lower electric field gave a smaller increase in shear stress depending on the electric-field strength, while the larger electric fields above a critical strength tended to give a larger stress response. The maximum shear stress enhanced by the electric fields in the present experiment was in excess of 10 times the steady shear stress under no electric field. The ER effect was discussed in terms of the Miesowicz viscosities, the interaction among anisotropic domains, as well as the electrohydrodynamic instability.