To provide a water/oil repellent composition which can impart water/oil repellency to a surface of an article without having its texture deteriorated, and has excellent durability against washing and stability, a method for producing such a composition, and an article treated with such a water/oil repellent composition.A water/oil repellent composition which comprises a copolymer having polymerized units derived from monomer (a), polymerized units derived from monomer (b) and polymerized units derived from monomer (c). Here, monomer (a) is a compound represented by the formula: (Z—Y)nX; wherein Z is a C1-6 perfluoroalkyl group or the like; Y is a bivalent organic group or a single bond; n is 1 or 2; and X is a polymerizable unsaturated group; monomer (b) is a (meth)acrylate having no Rf group and having a C12-18 alkyl group; and monomer (c) is monomer (c1) having no Rf group and having a blocked isocyanate group or monomer (c2) having no Rf group and having at least two polymerizable unsaturated groups.