Provided are a negative active material, a method of preparing the same, and a lithium battery including the negative active material. The negative active material includes a carbonaceous core that has a sulfur content of about 10 ppm to 900 ppm; and an amorphous carbon layer continuously formed on a surface of the carbonaceous core, wherein the carbonaceous core has a crystalloid plate structure, and a crystallite size measured from a full width at half maximum of the peak with respect to the surface (002) of about 10 nm to about 45 nm in an X-ray diffraction spectrum of the carbonaceous core. The lithium battery including a negative electrode including the negative active material has improved capacity characteristics and ring lifetime characteristics.