PURPOSE: To produce a thermoplastic ultrathin film by superposing a base layer on a coating layer so that a surface subjected to corona discharge treatment comes to the area between the base layer and the coating layer to form a composite film and biaxially stretching the composite film to delaminate the same and to obtain satisfactory running properties and thickness uniformity.

CONSTITUTION: A base layer and a coating layer are superposed one upon another by a usual method so that a surface subjected to corona discharge treatment comes to the area between the base layer and the coating layer. Thereafter, this composite web is biaxially stretched by a known method until the thickness of the coating layer becomes below 3 μm. Subsequently, the composite web is delaminated into the base layer and an ultrathin coating layer by a known method and the respective layers are separately taken up. As a result, a ultrathin film made of polyester with a thickness of 0.5-3 μm having very good running properties and an excellent thickness profile is obtained. Further, this ultrathin film has extremely high gloss and extremely slight fog.