Reflection of an Alfv¿n wave incident on an open magnetopause from the magnetospheric side is examined. An open magnetopause, whose structure is different from the standard rotational discontinuity, is assumed to be a parameterized discontinuity with a nonzero normal field component. When an Alfv¿n wave is incident on the open magnetopause, reflected and transmitted waves are generated. The emanating wave can be analyzed using linearized MHD conservation relations across the magnetopause, together with Snell's law. Under the assumption that the magnetic fields on the two sides of the open magnetopause are coplanar with the normal direction of the magnetopause, the governing equations are solved numerically. Our results show that the electric fields of emanating Alfv¿n wave depend mainly on the number density and the magnetic field jumps across the magnetopause. Under conditions representing the open magnetopause, it turns out that the open magnetopause behaves like a near perfect reflector. The corresponding reflection coefficient for the wave electric fields can be approximated by RE=Eir/Ei≈-1 as has been deduced by Kan and Sun (1985) based on physical arguments. In other words, the solar wind flow is more or less unchanged by the loading effect of the Alfv¿n wave incident on the magnetopause from the magnetospheric side. Therefore, under the assumptions of our model, the open magnetopause can be viewed as a constant voltage source. ¿ American Geophysical Union 1990