Abstract: Effect of elastic cavity walls on acoustic characteristics of a water-filled Helmholtz resonator is investigated. A theoretical model based on equivalent lumped parameter assumption is developed to take into account the elasticity of the cylindrical cavity walls. The resonance frequency of the Helmholtz resonator, transfer-function between excited pressure and cavity pressure, and sound transmission loss along a water-filled duct connected with the elastic Helmholtz resonator are studied. An experiment is also carried out on the Helmholtz resonator to validate numerical predictions. The differences between rigid and elastic cavity walls are presented. Both theoretical and experimental results conclude that the elasticity of cavity walls significantly affect the acoustic performance of the Helmholtz resonator.