PURPOSE: To provide a battery mounting structure capable of surely fixing a battery and improving its mounting/demounting workability and excellent in cooling performance of the battery.

CONSTITUTION: A battery unit 8 is constituted by arranging batteries 7, formed in a columnar shape, horizontally fitted in a battery receiving window 4 formed in each crossing part between horizontal/vertical plate materials 2, 2 and 3, 3 of a battery mounting rack 1 formed into a parallel crosses shape by the horizontal/vertical plate materials 2, 2 and 3, 3. The battery mounting rack 1 is fixedly fastened to a car body side member to be mounted on a car body. By forming the battery mounting rack 1 into a parallel crosses shape and by arranging the battery 7 exposed, the battery 7 is totally exposed in cooling air circulated in the axial direction of the battery mounting rack 1, to improve cooling performance of the battery 7.