his paper presents a simultaneous optimization approach to the design of the multiple active tuned mass damper (MATMD) and its controller for building vibration attenuation under seismic excitations. A model of an n-storey building installed with the MATMD system, where the masses can be placed on different storeys, is considered, and its state-space model is established by appropriately defining the state variables and the output signals. Considering that earthquake records exhibit higher strength over a certain range of frequency and the fact that not only the controller design but also the parameter optimization of the MATMD system have significant effects on the control performance, a simultaneous optimization approach based on the genetic algorithm (GA) is proposed to design the static output-feedback controller and to obtain the MATMD's parameters for the attenuation of seismic building vibration over a finite frequency range. Using the proposed approach, a set of parameters and the constrained controller gains, which can guarantee the asymptotic stability of the closed-loop system and attenuate the building vibration at a sufficiently low level, are obtained. Simulations are used to demonstrate the effectiveness of the proposed approach and the superiority of a strategy that places the masses on different storeys in attenuating building vibration under earthquake excitation.