A cathode active material for a lithium rechargeable battery is provided. The cathode active material is used for a lithium rechargeable battery containing a cathode, an anode, and an electrolytic solution. The cathode active material is composed of 0.5% by weight or less carbonate ion (CO.sub.3.sup.2-) plus bicarbonate ion (HCO.sub.3.sup.-) and 0.1% by weight or less hydroxyl ion (OH.sup.-). The swelling of lithium battery containing the cathode active material is substantially suppressed when is placed at 60.degree. C. or more.