A metal-air battery including: a negative electrode metal layer; a negative electrode electrolyte layer disposed on the negative electrode metal layer; a positive electrode layer disposed on the negative electrode electrolyte layer, the positive electrode layer comprising a positive electrode material which is capable of using oxygen as an active material; and a gas diffusion layer disposed on the positive electrode layer, wherein the negative electrode electrolyte layer is between the negative electrode metal layer and the positive electrode layer; wherein the negative electrode metal layer, the negative electrode electrolyte layer, and the positive electrode layer are disposed on the gas diffusion layer so that the positive electrode layer contacts a lower surface and an opposite upper surface of the gas diffusion layer, and wherein one side surface of the gas diffusion layer is exposed to an outside.