A new seismic stiffness design method is developed for a building frame-pile-soil system. The interaction system consists of a representative frame, a pile and a free-field soil model. A closed form solution is derived to a hybrid inverse eigenmode problem for a specified fundamental frequency and eigenmode strain. The solution is shown to be useful and efficient for developing a direct method of seismic stiffness design of the building frame-pile-soil system. This is essentially a procedure for solving a hybrid inverse problem such that the member stiffnesses are to be found for specified mean maximum member strains or stress ratios and for a specified pile-soil system under design spectrum-compatible earthquakes. Design examples are presented to demonstrate the usefulness of this design method. Time-history analysis is performed to demonstrate the validity and accuracy of this design method.