The present invention provides a lithium-nickel-manganese-cobalt composite oxide in which the reactivity between a lithium raw material and a metal composite hydroxide is improved so that a high low-temperature output characteristic can be achieved, a method for manufacturing the composite oxide, and a positive electrode active material and the like without causing a problem of gelation during the paste preparation. A positive electrode active material for non-aqueous electrolyte secondary batteries, including a lithium-metal composite oxide powder including a secondary particle configured by aggregating primary particles containing lithium, nickel, manganese, and cobalt, or a lithium-metal composite oxide powder including both the primary particles and the secondary particle. The secondary particle has a solid structure inside as a main inside structure, the slurry pH is 11.5 or less, the soluble lithium content rate is 0.5 [% by mass] or less, and the specific surface area is 1.0 to 2.0 [m2/g].