There is provided a positive electrode active material composite for a lithium-ion secondary battery, in which, when using as a positive electrode active material of the lithium-ion secondary battery, it can effectively improve high-temperature cycle characteristics. In the positive electrode active material composite for a lithium-ion secondary battery, only on the surface of a lithium transition metal oxide secondary particle (A) composed of one or more of the lithium transition metal oxide particles represented by the following formula (I): LiNiaCobMncM1xO2 . . . (I) or the following formula (II): LiNidCOeAlfM2yO2 . . . (II), a lithium-based polyanion particles (B) is composited with lithium transition metal oxide particles under a specific condition, the lithium-based polyanion particles (B) being represented by the following formula (III) or (III)′: LigMnhFeiM3zPO4 . . . (III) or Mnh′Fei′M3z′PO4 . . . (III)′ and being supporting carbon (C) on a surface thereof.