In a battery mount structure wherein a battery carrier 5 with a battery 3 housed interiorly is arranged below a passenger step 19 to a vehicle, a battery cover 8 is adapted to be movable toward and away from the vehicle in the widthwise direction of the vehicle. In the battery cover 8, a top face member 8a of the battery cover 8 has an end adjacent to a chassis frame 1 which is adapted to be engaged with locked portions 6a and 6b on a back plate 4c of a battery carrier body 4. An end of the battery cover 8 away from the chassis frame 1 is provided with a front wall 8b having a locking portion 10, the locking portion 10 being adapted to be engaged with a locked portion 4d' of the battery bracket 4d.