Abstract: Provided is a use for a peptide in surface-treating a medical device or medical material to be used in contact with blood, with which it is possible to obtain a medical device or medical material that can achieve highly efficient vascular endothelialization through the use of a peptide uniquely binding to vascular endothelial cells. Also provided are: a peptide suitable for use in said surface treatment; a method for producing a medical device or medical material surfaced-treated with said peptide and to be used in contact with blood; and a surface treatment agent including said peptide, said agent to be used in surface-treating a medical device or medical material to be used in contact with blood. In the present invention, a medical device or medical material is surface-treated using a peptide that includes any one of ten specific amino acid sequences and uniquely binds to the surface of endothelial progenitor cells.