A treatment agent for fiber products, represented by general formula (I), comprising a combination of a modifier comprising a fluorinated phosphate derivative having a molecular weight of 2,000 or less or a salt thereof with a fixing agent comprising a metal salt compound, wherein R?1 and R2¿ may be the same or different from each other and each represents hydrogen or R¿f?-(CH2)m-, provided that not both of R?1 and R2¿ are hydrogen at the same time; A represents oxygen, sulfur or a direct bond; and n is 1 or 2. A method of treating fiber products with the treatment agent and, if necessary, a fluorinated water and oil repellent or a fluorinated antisoiling finish. Fiber products can retain inherent touch, hand, hue and flexibility even after the treating and use thereof, including washing and friction, and can be endowed with hot water repellency and persistent water and oil repellency.