A trial study to examine if the sound reduction effects in the rocket fairing are obtained or not was carried out by using, so to speak, Sound Decreasing Structure, considering that concerned Structure is very similar to the structure of existing rocket faring. Specimens are honeycomb sandwich plate structures composed of outer thin Al skin and inner porous Al of sound absorbing material in stead of Al skin. They were excited acoustically by white random noise in the rectangular acoustic tube and the transmitted SPL was measured in the anechoic chamber and compared with the excitation SPL. As a result, it turned out that sound decreasing effects were actually observed if the SPL is normalized by the velocity SPL of specimens. And besides if the sound absorbing effects of reflection sounds from the inner walls of faring model are added in addition to the above decreasing ones by setting the concerned models on all surrounding walls in the chamber, it was observed that SPL reduction effects were remarkably large in the low frequency range that is important from the practical point-of- view of breakage of satellite components.