A case for a battery pack includes a first case member including a first sidewall, a first rib extending from the first sidewall, and a coupling hook disposed on the first rib and a second case member including a second sidewall, a second rib spaced from and parallel to the second sidewall, a coupling hole defined in the second rib and coupled to the coupling hook. The first rib includes a reinforcement part disposed on an inner surface thereof facing the second rib.