The main function of building wall components was to separate spaces with different functions. Lightweight partition walls were commonly used constructions, consisting primarily of light steel or wooden studs combined with wall panels. As these structures can be prefabricated and assembled on site, the influence of on-site construction conditions was reduced, and less labor was required. Consequently, this type of wall had been widely applied in Taiwan. A cavity was a characteristic feature of lightweight partition walls, providing both sound and thermal insulation. In this study, the effects of cavity size and different wall panel combinations on the airborne sound insulation performance of lightweight partition walls were investigated, and an optimized wall structure was developed. The experiments in this study were conducted at Pingtung University of Science and Technology in Taiwan, and the wall specimen area complied 10.2 m² with ISO 10140-2 standard. The results showed that the airborne sound insulation performance of lightweight partition walls was directly proportional to the surface density of the wall panels, and that increasing the cavity size enhanced sound insulation values at frequencies above 500 Hz. An optimized wall design with a double cavity was developed, achieving an airborne sound insulation performance of 55 dB, which may serve as a reference for building design practice.