A negative active material and a lithium battery including the negative active material. The negative active material includes primary particles, each including: a crystalline carbonaceous core having a surface on which silicon-based nanowires are disposed; and an amorphous carbonaceous coating layer that is coated on the crystalline carbonaceous core so as not to expose at least a portion of the silicon-based nanowires. Due to the inclusion of the primary particles, an expansion ratio is controlled and conductivity is provided and thus, a formed lithium battery including the negative active material may have improved charge-discharge efficiency and cycle lifespan characteristics.