A negative active material for a lithium secondary battery and a lithium secondary battery including the same are provided. The negative active material may be a silicon (Si)-based alloy negative active material. In some embodiments, the Si-based alloy negative active material may include Si, iron (Fe), copper (Cu), and aluminum (Al), and may have a Si single phase and a first alloy phase, the first alloy phase being represented by a formula of AlxCuy, where x