A positive active material for a rechargeable lithium battery includes a first compound represented by Chemical Formula 1 and a second compound represented by Chemical Formula 2, the second compound having a smaller particle size than that of the first compound, wherein cation mixing in the surface portion of the positive active material is less than or equal to about 7.5%, cation mixing in the bulk of the positive active material is less than or equal to about 3%, a residual lithium content on the surface of the positive active material is less than or equal to about 3,000 ppm, and the first compound and the second compound each independently include 90 at % to about 98 at % of Ni with respect to the metals excluding Li. Lia1Nix1Coy1M11−x1−y1O2,  Chemical Formula 1 Lia2Nix2Coy2M21−x2−y2O2.  Chemical Formula 2