In this paper, several properties of endomorphism rings of modules are investigated. A multiplication module M over a commutative ring R induces a commutative ring <TEX>$M^*$</TEX> of endomorphisms of M and hence the relation between the prime (maximal) submodules of M and the prime (maximal) ideals of <TEX>$M^*$</TEX> can be found. In particular, two classes of ideals of <TEX>$M^*$</TEX> are discussed in this paper: one is of the form <TEX>$G_{M^*}\;(M,\;N)\;=\;\{f\;{\in}\;M^*\;|\;f(M)\;{\subseteq}\;N\}$</TEX> and the other is of the form <TEX>$G_{M^*}\;(N,\;0)\;=\;\{f\;{\in}\;M^*\;|\;f(N)\;=\;0\}$</TEX> for a submodule N of M.