A method for manufacturing an aluminum heat exchanger includes the steps of: obtaining a heat exchanger tube 2 by forming a Zn thermally sprayed layer on a surface of an aluminum flat tube core so as to adjust Zn adhesion amount to 1 to 10 g/m.sup.2; obtaining a heat exchanger core by alternatively arranging the heat exchanger tube 2 and an aluminum fin 3 and brazing the heat exchanger tube and the fin with end portions of the heat exchanger tube connected to aluminum headers in fluid communication; and forming a chemical conversion treatment coat (corrosion resistance coat) on a surface of the heat exchanger core by subjecting the surface of the heat exchanger core to chemical conversion treatment using at least one chemical conversion treatment agent selected from the group consisting of phosphoric acid chromate, chromic acid chromate, phosphoric acid zirconium series, phosphoric acid titanium series, fluoridation zirconium series, and fluoridation titanium series. The obtained heat exchanger has a long last good corrosion resistance and can prevent occurrence of fin detachment and pit corrosion.