There is disclosed a rust prevention and hydrophilization treatment method for a flux-brazed aluminum-made heat exchanger which comprises subjecting the same to a rust prevention treatment by the use of a zirconium base compound and/or a titanium base compound, and thereafter subjecting the same to a hydrophilization treatment by means of a hydrophilization treatment agent composition containing the under-mentioned components:

(1) 40 to 90% by mass of polyvinyl alcohol having a degree of saponification of at least 90% ;
(2) 3 to 40% by mass of polyoxyalkylene-modified polyvinyl alcohol in which 0.01 to 20% of pendant groups are polyoxyalkylene ether groups;
(3) 1 to 30% by mass of an inorganic cross-linking agent which reacts with hydroxyl groups of the polyvinyl alcohol and modified polyvinyl alcohol; and
(4) 1 to 20 % by mass of a guanidine compound and / or a salt thereof.

The above simplified method dispenses with a flux removal step without causing wastewater treatment problems, and thus assures favorable rust prevention and deodorization effects.