To provide a cathode active material for a lithium secondary battery capable of improving load characteristics such as high capacity and rate-output characteristics and reducing its cost and coping with both high-voltage resistance and a high level of safety.

The cathode active material for a lithium secondary battery is composed of laminar lithium nickel manganese cobalt-based composite oxide in an excessive Li state heat-treated under a carbon dioxide-contained atmosphere. When the carbonate ion concentration measured by an ion chromatography is c wt.% and a specific surface area measured by a BET method is S m2/g, a c/S value is 0.055 or more and 0.30 or less.