This positive electrode active material for nonaqueous electrolyte secondary batteries is a positive electrode active material that comprises a lithium transition metal composite oxide containing at least 80 mol % Ni with reference to the total number of moles of metal elements excluding Li, and that has B present on the particle surface of at least this composite oxide. Assuming that a particle having a particle diameter larger than the 70% volume-based particle diameter (D70) is denoted as a first particle and a particle having a particle diameter smaller than the 30% volume-based particle diameter (D30) is denoted as a second particle, the mole fraction of B, with reference to the total number of moles of metal elements excluding Li, in the first particle is larger than the mole fraction of B, with reference to the total number of moles of metal elements excluding Li, in the second particle.