The invention relates to a flat tube for a heat exchanger formed by folding one plate or overlaying two plates, in which long beads (16) are formed in multiple rows on the plate in its longitudinal direction, portions of the plate to which the respective long beads are opposed are formed flat, the tops of the long beads are joined with the flat portions (15) to form a plurality of channels (17) by the long beads and the flat portions, and a plurality of passages (18) which communicate adjacent channels are formed at appropriate parts on the long beads formed in the longitudinal direction of the plate. The invention also relates to a method for producing the above tube. Thus, the plates can have their faces securely engaged, and a heat exchanger having an improved heat-exchanging efficiency can be obtained.