In an aspect, a negative active material, a method of preparing the negative active material, and a lithium battery including the negative active material are provided. The method of preparing the negative active material may increase pulverizing efficiency in pulverizing a silicon-based bulky particle into a nano-size silicon-based primary particle and decrease a capacity loss of the obtained negative active material. The nano-size negative active material has excellent crystalline characteristics, high capacity, and high initial efficiency, due to a decrease in surface oxidation and surface damage.