[Problem to be Solved]There can be provided a lithium secondary battery which, when used as a positive electrode active material for lithium secondary batteries, is particularly excellent in cycle characteristics and rate characteristics and low in direct current (DC) resistance and in which the swelling resulting from the generation of gas accompanying the reaction with a nonaqueous electrolyte solution is suppressed. There is also provided a positive electrode active material for lithium secondary batteries in which the positive electrode active material can be industrially advantageously produced.[Solution]The positive electrode active material for lithium secondary batteries according to the present invention includes a lithium-transition metal composite oxide containing from 0.20 to 2.00% by weight of Ti atoms, which is produced by mixing a lithium compound, a cobalt compound and titanium dioxide and then firing the resulting mixture, wherein the Ti atoms are present in the depth direction from the surface of the particles of the lithium-transition metal composite oxide and have a concentration gradient that is highest at the surface of the particles.