A method of producing an aluminum alloy heat-exchanger is disclosed, wherein, upon producing an aluminum alloy heat-exchanger by soldering technique, it is retained for 10 minutes to 30 hours at 400.degree. to 500.degree. C. after finishing a heating for soldering. It is better to retain the heat-exchanger during cooling. Alternatively, the heat-exchanger may be cooled to 150.degree. C. or lower and reheated to 400.degree. to 500.degree. C. for at least 10 minutes to up to 30 hours. Furthermore it is preferable to cool at a cooling velocity of not slower than 30.degree. C./min across a temperature range from about 200.degree. C. to about 400.degree. C. after the retainment. Excellent thermal efficiency, high strength and excellent corrosion resistance can be achieved this way.