In recent years, structure-bone sound generated by water piping system influences on the rooms in hotels and apartment houses etc, and a problem caused by the noise are increasing. So the experimental investigations on the sound and vibration reduction of structure-bone sound at water piping systems by two size of expansion chamber type mufflers were carried out. The following conclusions were obtained. As the result, it was shown that calculation values by plane wave theory on sound transmission loss of two size of expansion chamber type mufflers and experiment values were in good agreement comparatively at frequency bands which resonance frequencies of longitudinal wave of inner water are not included.