In a battery mounting structure for a vehicle that includes a battery box mounted on an under-floor side of a vehicle body floor, the battery box includes: a battery pan on which a battery is placed; an outer peripheral frame formed to project from an outer peripheral edge portion of the battery pan; a cover placed on the battery pan from above; and sealing means provided in a joint portion between the battery pan and the cover, wherein the sealing means is disposed above the outer peripheral frame and positioned further inside than an outer periphery of the outer peripheral frame in plan view.