To provide a lithium secondary battery which has high capacity while maintaining excellent charge-discharge characteristic, and to provide a cathode of the lithium secondary battery and a plate-like particle for cathode active material to be contained in the cathode. The plate-like particle of cathode active material for a lithium secondary battery of the present invention has a layered rock salt structure, a thickness of 5 μm or more and less than 30 μm, 2 or less of [003]/[104] which is a ratio of intensity of X-ray diffraction by the (003) plane to intensity of X-ray diffraction by the (104) plane, a voidage of 3% or more and less than 30%, and an open pore ratio of 70% or higher.