The purpose of this study is to develop structral technologies on the lightweight composite slab systems with sound reduction layers in the modular house. In this study, two kinds of slabs with minimum thickness was suggested reducing the floor impact sound. In order to evaluate the structural performance, the flexural strenth tests were carried out on the one-way full scale specimens. From the results of test, we know that the proposed slabs had ductile behavior and would be safe sufficiently.