Disclosed are a positive active material for a rechargeable lithium battery, a preparation method thereof, and a rechargeable lithium battery including the same. The positive active material for a rechargeable lithium battery includes a first positive active material including a lithium nickel-based composite oxide and including a secondary particle in which a plurality of primary particles are aggregated and a cobalt coating portion on a surface of the secondary particle, and a second positive active material including a lithium nickel-based composite oxide and including a single particle and a cobalt coating portion on a surface of the single particle, wherein a cobalt content (at %) based on the total amount of nickel and cobalt in the cobalt coating portion of the first positive active material is about 1.45 times to about 1.60 times a cobalt content (at %).