An acoustic leaky mode resonator having a structure similar to that of an optical guided-mode resonator is demonstrated experimentally and theoretically. The measured transmission spectra reveal the existence of resonant modes and agree with the predictions of finite-difference time-domain calculations. The resonant modes were investigated by calculating the displacement and the pressure field. The relationship between the resonant frequency and the geometric parameters of the structures was studied. The results can be applied to the design of a narrow pass band acoustic filter.