A metal-air battery includes: at least one positive electrode layer, which is configured for using oxygen as an active material and includes a first surface and a second surface opposite the first surface; a gas diffusion layer on the first surface of the positive electrode layer and including a plurality of carbon fibers; an electrolyte layer on the second surface of the positive electrode layer; and a negative electrode metal layer on the electrolyte layer, wherein the positive electrode layer includes a plurality of grooves, and wherein portions of the plurality of carbon fibers are in the grooves.