To provide a hydrophilic surface treatment agent that is used for the hydrophilic surface treatment of heat exchangers, and enables good drainage to be sustained. A hydrophilic surface treatment agent for aluminum-containing metal heat exchangers is characterized by being formed by blending in: a water-soluble resin having a functional group comprising at least one of an amide group, a hydroxyl group and a carboxyl group, or a water-soluble resin having an amide bond in a skeleton (A); colloidal silica (B); an organoalkoxysilane and/or a hydrolysate thereof (C); a cross-linking agent (D) capable of cross linking with the water-soluble resin (A); and water (E). The hydrophilic surface treatment agent for aluminum-containing metal heat exchangers is further characterized in that: {(B)+(C)}/{(A)+(B)+(C)+(D)} is 0.1 to 0.5 in terms of the ratio (mass ratio) of solids; and (C)/(B) is 0.5 to 4.0 in terms of the ratio (mass ratio) of solids.