Provided is a metal oxygen battery 1 including a positive electrode 2 having oxygen as an active material, a negative electrode 3 having metallic lithium as an active material, and an electrolyte layer 4 interposed between the positive electrode 2 and negative electrode 3. The positive electrode 2 contains oxygen storage material including mixed crystal of hexagonal composite metal oxide expressed by the general formula AxByOz (in which, A is one type of metal selected from a group of Y, Sc, La, Sr, Ba, Zr, Au, Ag, Pt, Pd, B is one type of metal selected from a group of Mn, Ti, Ru, Zr, Ni, Cr, and x=1, 1≦y≦2, 1≦z≦7, provided that a case where both A and B are Zr is excluded) and one or more non-hexagonal composite metal oxide expressed by the general formula AxByOz.