Provided is a positive electrode active material for nonaqueous electrolyte secondary batteries that suppresses the gelling of a positive electrode mixture material paste and has high weather resistance, a production method thereof, and the like. A method for producing a positive electrode active material for nonaqueous electrolyte secondary batteries includes cleaning a powder famed of a lithium-nickel composite oxide represented by a general formula LizNi1-x-yCoxMyO2 where 0≤x≤0.35; 0≤y≤0.10; 0.95≤z≤1.10; and M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti, and Al with an aqueous solution containing one or more lithium salts selected from water-soluble lithium salts other than lithium hydroxide and drying the cleaned powder.