A negative active material for a rechargeable lithium battery and a rechargeable lithium battery including the same are disclosed, and the negative active material includes a primary particle of a crystalline carbon-based material and secondary particle that is an assembly of the primary particles, wherein a ratio of an average particle diameter (D50) of the secondary particle relative to an average particle diameter (D50) of the primary particle (average particle diameter (D50) of the secondary particle/average particle diameter (D50) of the primary particle) ranges from about 1.5 to about 5 and an aspect ratio of the primary particle ranges from about 1 to about 7.