The present disclosure discloses a battery pack suitable for improving cooling efficiency of a cooling duct for battery cells in a battery module by reducing a sealing area between a lower case and an upper case configured to fully surround the battery module. The battery pack according to the present disclosure includes a battery module including battery cells sequentially stacked and a cooling duct located on side of the battery cells; a lower case configured to load the battery module and the cooling duct therein; and an upper case coupled to the lower case so as to cover the battery module and the cooling duct, the upper case having a vent structure on the cooling duct. The vent structure has, on the cooling duct, an inner air passage unit opened at a sidewall of the upper case, and an outer air passage unit inserted into the inner air passage unit.