A substrate for biochips, in which carboxyl groups are immobilized on a substrate whose surface at least is composed of carbon; and a method for producing the substrate are disclosed. The substrate for biochips comprises a substrate whose surface at least is composed of carbon; and an acrylic polymer having free carboxyl groups in the molecular structure thereof, which acrylic polymer is immobilized on the surface of the substrate. The method for producing the substrate comprises irradiating the substrate whose surface at least is composed of carbon with ultraviolet light during the acrylic polymer having free carboxyl groups in the molecular structure thereof contacts the substrate.