The present invention provides a battery box component which is obtained by providing a fiber-reinforced plastic with a refractory layer, said fiber-reinforced plastic using a thermosetting resin as a matrix resin, while containing reinforcing fibers, wherein: the reinforcing fibers are discontinuous reinforcing fibers having a weight average fiber length of from 1 mm to 100 mm; the thermosetting resin is composed of at least one resin that is selected from the group consisting of an unsaturated polyester resin, a vinyl ester resin, and an epoxy resin; the thickness X of the fiber-reinforced plastic is not less than 1.0 mm but less than 5 mm; and the refractory layer contains an acrylic resin or a urethane resin and a foaming composition. The present invention also provides a method for producing a battery box component.