The method of charging a lithium ion secondary battery uses a lithium ion secondary battery comprising a positive electrode including a mixed metal oxide containing at least Li, Mn, and Ni as metal components as a positive electrode active material, a negative electrode, and a nonaqueous electrolytic solution containing a lithium salt; and includes a constant current charging step of carrying out constant current charging with a set charging current value I1 corresponding to a set value nC satisfying the condition represented by the expression of 2C.ltoreq.nC.ltoreq.60C, where C is a rated capacity value of the lithium ion secondary battery, and n is a number of 2 to 60.