In reinforced concrete apartment buildings, the floor impact sound from the floor above can easily transfer to the house below. The number of environmental grievances due to floor impact sound occurring in apartment buildings is rapidly increasing in Korea. In order to reduce floor impact sound in apartment buildings, resilient damping materials placing between slab and finishing material offer a simple but effective solution. Korean standards association have established several standards on resilient damping materials to control their material qualities. This paper presents the test results of the properties of resilient damping materials subjected to long-term load. The experimental program involved conducting twenty four material tests under short-term load and thirty two specimens under long-term load. Three main parameters were considered in the experimental investigation: the eight types of resilient materials, weight of load, and loading periods. This experimental test focused specifically on the observation of the deflection and dynamic elastic modulus of resilient materials subjected to long-term load. Test results indicated that the duration of load strongly effects on the properties of resilient materials for reduction of floor impact sound.