A positive electrode active material for a nonaqueous electrolyte secondary battery contains silicon and lithium nickel complex oxide having a layered rock-salt structure and is composed of secondary particles formed of aggregated primary particles. Lithium nickel complex oxide contains 80 mol % or more of nickel, based on the total amount of metal excluding lithium, silicon content is 0.6 mass % or less based on the total amount of the positive electrode active material, and a porosity of the positive electrode active material is 0% or more and 1% or less.