The development of packaging for an underwater acoustic sensor is a more complex task than package design for a typical microelectronic device because of the need to simultaneously protect the device from the environment while allowing interaction with it. A bio-inspired package, based on the hearing mechanisms in aquatic animals, has been developed for this purpose. The package will ensure reliability in the underwater environment while not interfering with the transmission of sound. The package is designed to contain a nanowire sensor in a fluid medium, leaving the wires free to move. Materials matching the acoustic impedance of seawater are incorporated to allow sound to penetrate the package. Acoustic properties of various materials were investigated using scanning acoustic microscopy for this application. A prototype package was fabricated, and tests were performed to evaluate the impedance match between the selected materials and seawater.