Disclosed herein is a battery module assembly including (a) two or more battery modules having cell units, each of which includes one or more battery cells, connected in parallel to one another, (b) a pair of an upper case and a lower case to surround an upper part and a lower part of the battery modules in a state in which the battery modules are erected on their sides, (c) a bus bar assembly disposed at a front of the battery modules to electrically connect the battery modules to one another in parallel, and (d) a fastening hole formed at a front of the upper case and/or a front of the lower case to position or fix the battery module assembly.