This article presents an experimental study of the performance of particle dampers under harmonic excitation. The effects of various system parameters—including particle size, container dimensions, intensity, and frequency of excitation—were investigated using a single degree-of-freedom building model under har monic base excitation. It is shown that particle dampers, even with a small mass ratio, can be very effective in attenuating the vibrations of lightly damped structures. An approximate method is provided to estimate, with reasonable accuracy, the response of a harmonically excited structure that is equipped with a particle damper operating in the vicinity of the optimum range of its system parameters.