A battery mounting structure is provided to prevent water intrusion into a clearance between a battery pack and a floor panel of a vehicle. The battery mounting structure comprises: frame members extending longitudinally on both sides of the vehicle; a floor panel disposed between the frame members; and a battery pack situated underneath the floor panel. A sealing member is interposed between a periphery of the battery pack and a portion extending from a member opposed to the battery pack, and a drain hole is formed in the sealing member to connect an inner side and an outer side of the sealing member.