PURPOSE: To impart excellent lipophilicity, hydrophilicity, etc., to the surface of a film made of a fluoropolymer by irradiating the film with ultraviolet in the presence of an amine to introduce (substituted) aminoalkyl groups as organic functional groups into the film surface.

CONSTITUTION: A film made of a fluoropolymer, e.g. a tetrafluoroethylene/ perfluoroalkoxyvinyl ether copolymer or polytetrafluoroethylene, is irradiated with ultraviolet in the presence of an amine to introduce organic functional groups selected from among (substituted) aminoalkyl groups into the irradiated area. Thus, chemical affinity such as lipophilicity or hydrophilicity is imparted to the film surface. Examples of the amine include primary, secondary, and tertiary (un)saturated alkylamines which are linear or branched, polyamines, and amines having substituents, e.g. hydroxyl and ester groups (e.g. triethylamine and polyethyleneimine).