A secondary air supply system for an internal combustion engine includes: a cylinder head of the internal combustion engine having a plurality of exhaust holes and a plurality of supply holes formed thereon; a supply path communicating the exhaust holes and the supply holes so as to supply secondary air into the supply holes; an exhaust manifold attached to the cylinder head, and provided with a flange having a plurality of communication holes penetrating the flange; a lower shell including connection holes respectively corresponding to the communication holes, the lower shell being secured to the flange such that the communication holes and the connection holes are aligned; and an upper shell combined with the lower shell so as to form the supply path, communicated with the plurality of connection holes, between the lower shell and the upper shell.