To provide excellent lithium-nickel composite oxide particles which have high environmental stability and are thus capable of suppressing generation of impurities due to absorption of moisture and a carbon dioxide gas, while being prevented from easy separation of a coating film because of high adhesion thereof and having lithium ion conductivity. Coated lithium-nickel composite oxide particles, which are obtained by coating the surfaces of lithium-nickel composite oxide particles with a predetermined coating material, have electrical conductivity and ion conductivity and are capable of suppressing permeation of moisture and a carbon dioxide gas. Consequently, the present invention is able to provide coated lithium-nickel composite oxide particles for positive electrode active materials of lithium ion batteries, which is excellent for use in lithium ion batteries.