To provide a water/oil repellent composition with which an article which has favorable water/oil repellency and washing durability, and into which infiltration of a coating liquid can be suppressed, is obtained, and which presents a low environmental impact, its production method and an article having its surface treated with the composition. A water/oil repellent composition comprising a copolymer (X) having structural units based on the monomer (a) and structural units based on the monomer (b), and an aqueous medium, wherein the mass average molecular weight of the copolymer is at least 60,000, and the proportion of the structural units based on the monomer (a) is 60 to 95 mass %. Monomer (a): by (Z—Y)nX, wherein Z is a e.g. C1-6 polyfluoroalkyl group, Y is e.g. a bivalent organic group having no fluorine atom, n is 1 or 2, and X is a polymerizable unsaturated group. Monomer (b): vinyl chloride.