A lithium secondary battery includes a cathode including a cathode active material including a lithium-transition metal composite oxide particle having a crystal grain size of greater than 500 nm measured through X-ray diffraction (XRD) analysis, and an anode disposed to face the cathode. The present invention provides a lithium secondary battery having improved life-span characteristics while suppressing gas generation due to crack of the particles by controlling the crystal grain size of the lithium-transition metal composite oxide particles.