A method of producing a layered structure lithium mixed metal oxide, including a step of calcining a lithium mixed metal oxide raw material containing a transition metal element and a lithium element in a molar ratio of the lithium element to the transition metal element of 1 or more and 2 or less, in the presence of an inactive flux containing one or more compounds selected from the group consisting of a carbonate of M, a sulfate of M, a nitrate of M, a phosphate of M, a hydroxide of M, a molybdate of M, and a tungstate of M, wherein M represents one or more elements selected from the group consisting of Na, K, Rb, Cs, Ca, Mg, Sr and Ba.