Let R be a commutative ring with unity, M a module over R and let S be a G-set for a finite group G. We define a set M S to be the set of elements expressed as the formal finite sum of the form s∈S mss where ms ∈ M . The set M S is a module over the group ring RG under the addition and the scalar multiplication similar to the RG-module M G defined by Kosan, Lee and Zhou in [9]. With this notion, we not only generalize but also unify the theories of both of the group algebra and the group module, and we also establish some significant properties of (M S)RG. In particular, we describe a method for decomposing a given RG-module M S as a direct sum of RG-submodules. Furthermore, we prove the semisimplicity problem of (M S)RG with regard to the properties of MR, S and G.