A positive electrode active material quality judgment method that can easily and accurately judge the quality of a positive electrode active material used in a non-aqueous electrolyte secondary cell without having to complete the positive electrode. The positive electrode active material quality judgment method includes: heating a positive electrode active material mainly made of a lithium nickel composite oxide to a temperature x (° C.) of 200° C. or higher and 400° C. or lower; measuring the amount of carbon dioxide gas generated from the heating; and the positive electrode active material as a suitable positive electrode active material when the positive electrode active material satisfies formulas 3 and 4: y