A positive electrode active material for a lithium secondary battery includes a lithium cobalt complex oxide containing an alkali earth metal and a transition metal in a predetermined mixture ratio. A method of preparing the positive electrode active material includes mixing a lithium salt, a transition metal precursor, and an alkali earth metal salt to form a mixture, and performing at least one thermal treatment on the mixture. A positive electrode for a lithium secondary battery includes the positive electrode active material, and a lithium secondary battery includes the positive electrode.