The main purpose of this thesis is to investigate the least proper class containing the classWS of R-modules determined by weak supplement submodules over a ring R, in particular, over hereditary rings. A submodule A of a module B has(is) weak supplement if and only if there exist a submodule V in B such that A + V . B and the intersection of submodules of A and V is small in B. The classWS does not form a proper class, in general. By extending the class WS, we obtained the least proper class containing the class WS of R-modules over hereditary rings. We investigate the homological objects of the least proper class. We determine the structure of elements of the proper class by submodules.