The nonlinear interaction of a rapidly rotating magnetosphere with the external supersonic plasma flow is investigated by using the three-dimensional global magnetohydrodynamic (MHD) simulation. The results of the simulations clearly indicate that various dawn-dusk asymmetries are generated due to the effect of the rotation. Particularly, the location of the plasmoid, which is generated in the tail region of the rotating magnetosphere, is quite different from the case without rotation. It is also found that distinctive magnetospheric structures such as the plasma disc are largely modified in response to the dynamic pressure in the external plasma flow.¿ 1997 American Geophysical Union