Let G be a finite p-group and k be a field of characteristic p. A topological space X is called an n-Moore space if its reduced homology is nonzero only in dimension n. We call a G-CW-complex X an n-Moore G-space over k if for every subgroup H of G, the fixed point set XH is an n(H)-Moore space in k-coefficients, where n(H) is a function of H. We show that if X is a finite n-Moore G-space, then the reduced homology module of X is an endo-permutation kG-module generated by relative syzygies. A kG-module M is an endo-permutation module if Endk (M) = M ⊗k M* is a permutation kG-module. We introduce the group of finite Moore G-spaces M(G) with addition given by the join operation and relate this group to the Dade group generated by relative syzygies.