Abstract: The purpose of the carried-out examinations was to verify the receiving sensitivity of the hydrophone placed inside a protective housing. In order to increase resistance to damage, the hydrophone Reson TC4032 has been adapted to work in difficult environmental conditions. Using a comparative method, we analyzed the receiving sensitivity within a predetermined frequency band. The experiment was carried with two hydrophones: the examined one, and a reference one. An underwater speaker with a function generator was used as the sound source. The studies have been conducted in a water tank under laboratory conditions. In situ studies have determined the decrease of the receiving sensitivity of the hydrophone equipped with the protective housing.