PURPOSE: To form a hydrophilic film having stable capacity for a long period of time to the surface of a base material, by reacting a hydrophilic coating composition having a complementary reactive functional group with a preformed functional group-containing cured film to bond the same to said film.

CONSTITUTION: In making the surface of an underground structural material, a transport pipe material or a medical material hydrophilic, an undercoat composition is applied to the surface of the base material and cured at ambient temp. or by heating. Thereafter, a top coat composition is applied to the cured film and reacted with the undercoat film at ambient temp. or under a heating condition and the unreacted top coat composition is removed by washing to form a hydrophilic surface. In this case, the undercoat composition is based on an oligomer or a resin containing at least one kind of a reactive functional group such as an isocyanate group, an epoxy group or an active hydrogen group. The top coat composition has a functional group complementarily reacting with the functional group possessed by the undercoat composition and is based on a hydrophilic compound or resin.