A tube for a heat exchanger is formed by bending a three-layer clad material of an aluminum alloy to have an overlapped portion. The three-layer clad material is formed by a core material layer containing Mg not smaller than 0.2 wt % after brazing, a brazing material layer on one surface of the core material layer, and a high melting-point material layer on the other surface of the core material layer. The brazing material layer has a thickness not smaller than 25 μm before the brazing, and has a melting point lower than 600° C. The high melting-point material layer has a melting point equal to or higher than 600° C. In addition, the brazing material layer and the high melting-point material layer opposite to each other in the overlapped portion are bonded by the brazing at a temperature not lower than 450° C. for a time within 12 minutes.