The present invention provides a positive electrode active material for a lithium ion battery having good battery performance can be provided. The positive electrode active material for a lithium ion battery is represented by; Compositional formula: Li x Ni 1-y M y O 2+± wherein M is one or more selected from Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Ga, Ge, Al, Bi, Sn, Mg, Ca, B, and Zr, 0.9 ¤ x ¤ 1.1, 0 < y ¤ 0.7, and 0.05 ¤ ± ¤ 0.2, and contains primary particles and has a tap density of 1.3 to 2.6 g/cm 3 . The average particle size of the primary particles is 0.3 to 3.0 µm and the specific surface area is 0.3 to 2.3 m 2 /g.
