A treatment agent for hydrophilicity preferable for aluminum materials used for heat exchanger parts and air filter parts of air cleaner which can maintain the deodorizing property and hydrohilicity even after a long-time use, and a method of preparing said treatment agent. A treatment agent for hydrophilicity according to this invention comprising silica particulates and polymer of vinyl alcohol series in the weight ratio in the range 30:70∼70:30, amounting to 0.2∼25 weight percent in total of both relative to the entire treatment agent, in which said silica particulates are coated with said polymer of vinyl alcohol series, and dispersed in aqueous medium as coated particles having the average particle diameter 5∼1000 nm.