Disclosed are a negative active material for a rechargeable lithium battery including a spherically-shaped natural graphite-modified composite particle including: a spherically-shaped natural graphite particle where flake-shaped natural graphite fragments build up and assemble into a cabbage or random shape; and amorphous or semi-crystalline carbon, wherein an open gap between the flake-shaped natural graphite fragments is positioned on a surface part or inside the spherically-shaped natural graphite particle, the amorphous or semi-crystalline carbon is coated on the surface of the spherically-shaped natural graphite particle, and the amorphous or semi-crystalline carbon is present in the open gap, and thereby the open gap positioned on the surface part and inside the spherically-shaped natural graphite particle is maintained, a method of preparing the same, and a rechargeable lithium battery including the same.