Disclosed is an electrode active material having a core-shell structure, which includes: (a) a core capable of intercalating and deintercalating lithium ions; and (b) a shell including a polymer or an oligomer having a glass transition temperature of 25° C. or less when impregnated with an electrolyte, wherein a surface of the core is coated with the shell. Also, an electrode manufactured by using the electrode active material and a secondary battery including the electrode are disclosed. The shell (b) suppresses the formation of an SEI layer during initial charge of a battery, and prevents initial capacity reduction. Accordingly, it is possible to achieve a high capacity battery. The electrode active material having a core-shell structure, specially a metal (loid) based electrode active material having a core-shell structure can have a slightly higher electric capacity, compared to a conventional electrode active material, specially a conventional metal (loid) based electrode active material, and can minimize gas generation during charge/discharge.