Disclosed is a lithium mixed metal oxide which is useful for a positive electrode active material that is capable of providing a nonaqueous electrolyte secondary battery having more excellent cycle characteristics, in particular, more excellent cycle characteristics during high-temperature operation at 60 DEG C. or the like. Specifically disclosed is a lithium mixed metal oxide represented by the following formula (A). Lix(Mn1-y-zNiyFez)O2 (A) (In the formula, x is not less than 0.9 and not more than 1.3; y is 0.46 or more and less than 0.5; and z is 0 or more and less than 0.1.) Also disclosed are: a positive electrode active material which comprises the lithium mixed metal oxide; a positive electrode which comprises the positive electrode active material; and a nonaqueous electrolyte secondary battery which comprises the positive electrode.