This invention provides a base material comprising a plastic-containing support and, on its surface, a hydrophilic layer comprising an ethylene glycol chain (an EG chain) composed of one or more ethylene glycol units, as well as a method for producing such base material. A polysiloxane-containing primer layer is provided on the support comprising a plastic material on its surface, and the EG chain is covalently bound to a polysiloxane side chain of the primer layer. Thus, a hydrophilic layer comprising the EG chain can be provided on the surface of the plastic-containing support.