To provide a fluorinated copolymer and a water/oil repellent composition, whereby adequate water/oil repellency and excellent dynamic water repellency are obtainable and environmental impact is low. A fluorinated copolymer comprising units (A1) derived from a macromonomer wherein the average polymerization degree of e.g. 2-perfluorohexylethyl acrylate is from 20 to 30, and units (B) derived from a monomer (b) which has no fluoroalkyl group and no cross-linkable functional group and of which the glass transition temperature, when formed into a homopolymer, is from 50 to 150° C., wherein the average polymerization degree of the macromonomer per one molecule of the fluorinated copolymer is at least 1, and a water/oil repellent composition containing such a fluorinated copolymer.