In a tube (4) for a heat exchanger comprising a flat pipe (16) whose both ends are opened and in which a flow path (15) for a heat exchanging medium is formed, and an inner fin (17) arranged in the flow path (15), wherein said flat pipe (16) is constituted of a sheet of material for a flat pipe, the inner fin is constituted of two opposing flat plate portions (17b, 17c) connected along one of side edges of said flat pipe (16) and formed in a flat plate shape so as to be in contact with an inner surface of the said flat pipe (16), and projection portions (17d) which are projected from at least one of the flat plate portions (17b, 17c) and whose tops are in contact with the other opposing flat plate portion (17b, 17c). It is preferred that the projection portions (17d) are projected from both of the flat plate portions (17b, 17c) toward the opposing flat plate portion, and the opposing tops are made come in contact with each other. The tube for a heat exchanger which can prevent significant deformation of the inner fin from occurring when the inner fin included in the flat pipe is cut in a width direction thereof together with the flat pipe can be provided.