Provided are methods for surface-modifying a thermoplastic resin which produce surfaces that show not only low adsorption of proteins and cells but also selective adsorption or adhesion of specific cells such as cancer cells, and further have excellent durability. A method for surface-modifying an object made of a thermoplastic resin, the method including: step 1 of forming polymerization initiation points on the surface of the object; and step 2 of radically polymerizing at least a hydrophilic monomer starting from the polymerization initiation points by irradiation with UV light having a wavelength of 300 to 400 nm to form a graft layer having a thickness of 2 to 100 nm on the surface of the object.