In the present paper the Plane Couette flow for three cases, (i) Walls at unequal temperatures, (ii) Walls at equal temperatures and (iii) One of the walls is insulated, has been studied by taking a non-linear relation between viscosity and temperature. Exact solutions of the conpled momentum and energy equations have been obtained. A modified law for the transfer of heat at the upper wall is found in the case of unequal wall temperatures.