Disclosed is an electrode active material comprising: a core layer capable of repeating lithium intercalation/deintercalation; an amorphous carbon layer; and a crystalline carbon layer, successively, wherein the core layer comprises at least two core particles. A secondary battery comprising the same electrode active material is also disclosed. The electrode active material can inhibit variations in volume of the core layer that may occur during repeated charge/discharge cycles, since the core layer comprising at least two core particles, each core particle having an increased area that is in contact with the carbon layer coated thereon. Therefore, the battery using the electrode active material can provide improved cycle life characteristics.