The seismic response of highrise structures and tall buildings under vertical ground motion is analyzed by using the step-by-step integration procedure and the response spectrum procedure in this paper. The analysis shows that the vertical seismic internal forces Nv cannot be neglected. In case where the degrees of the earthquake intensity over 8, Nv in the upper part of the structure could reach or exceed the internal forces Ng caused by gravity, and in the lower part Nv could reach 20-50 percent of Ng. Th...