The present invention provides a bus bar assembly, which is a member electrically connecting two or more cell module assemblies to each other in order to form a battery module assembly by laterally disposing the cell module assemblies such that the cell module assemblies come into close contact with or are adjacent to each other. The bus bar assembly comprises: (a) a cover plate made of an electrically-insulating material and mounted on the upper ends of the cell module assemblies; (b) two or more conductive connection parts electrically connected to the external input/output terminals of the cell module assemblies when the conductive connection parts are mounted on the cover plate; and (c) two or more bus bars vertically mounted on the upper end of the cover plate with respect to the direction in which the cell module assemblies are arranged so as to electrically connect the conductive connection parts of the cell module assemblies to each other.