A surface-treated plastic film having a surface coating layer formed on at least one surface of a plastic film, which has a spreading index of aqueous and alcohol inks of 1.0-1.2, respectively, at the surface coating layer side thereof, and an ink jet recording material. The surface-treated plastic film of the present invention having respective spreading indices of aqueous and alcohol inks of 1.0-1.2 allows less spreading of the aqueous ink of ballpoint pens, is superior in writability and offset printability, and is extremely useful as a synthetic paper. In addition, the use of such surface-treated plastic film enables production of an ink jet recording material permitting high grade recording.