The anticorrosion treatment method of the invention is carried out on the outer surface of an aluminum extruded heat exchange tube which is formed of an Al alloy containing Mn 0.2 to 0.3 mass %, Cu 0.05 mass % or less, and Fe 0.2 mass % or less, and which has a wall thickness of 200 μm or less. The anticorrosion treatment method includes applying a specific dispersion of a flux powder and a Zn powder onto the outer surface of the heat exchange tube, and vaporizing a liquid component of the dispersion, to thereby deposit the Zn powder and the flux powder on the outer surface of the heat exchange tube, such that the Zn powder deposition amount, the flux powder deposition amount, and the ratio of the flux powder deposition amount to the Zn powder deposition amount are adjusted to specific values.