A vehicle battery mounting structure includes a battery frame that is disposed at a vehicle lower side of a floor panel, and is made from resin; a ductile member that includes a main body joined to the battery frame and a flange contiguously formed at a vehicle width direction outside end of the main body, the flange having a hole, and the ductile member being fastened to a lower face of the floor panel using a fastener inserted through the hole; and a fastening portion that is formed in a region including the hole, having a substantially hat shaped cross-section profile projecting toward a vehicle upper side and having ridge lines on vehicle front-rear direction sides of the region, and the ridge lines being formed with curved or bent shape toward directions heading away from the hole on progression toward a vehicle width direction inside in plan view.