A battery case structure for a motorcycle can include a battery case for storing therein a battery to be mounted in a motorcycle, and a starter relay and a fuse box as related parts which can be connected to the battery. A starter relay mounting portion and a fuse box mounting portion in which the starter relay and the fuse box are disposed relative to the battery case are provided. A sub-case is disposed near the battery on an inside of a battery case main unit. The sub-case includes the starter relay mounting portion and the fuse box mounting portion.