To provide a water/oil repellent agent and a water/oil repellent composition which is capable of providing an article surface with a sufficient water/oil repellency, while placing little burden on the environment.One comprising a reaction product obtained by reacting a fluoromonool having a polyfluoroalkyl moiety having at most 6 carbon atoms as an alcohol, an alkane monool having at least 18 carbon atoms, and MDI or a polymeric MD, and by treating an article with such a water/oil repellent agent, a sufficient water/oil repellency can be imparted, while placing little burden on the environment. By treating the above-mentioned article with the water/oil repellent composition of the present invention, a high quality water/oil repellency can be imparted to the article.