Human CC chemokine receptor (CCR) 5 is a G protein-coupled receptor involved in a broad range of human diseases that mediates HIV-1 viral entry into cells. Certain small molecule receptor antagonists to CCR5 have been useful in therapy for these diseases. In this study, CCR5-expressing CHO cells (CHO/CCR5 cells) were used to select CCR5-binding peptides from a phage-displayed 12-mers peptide library. All of the 30 clones selected from the library showed specific binding to CHO/CCR5 cells by enzyme linked immunosorbent assay (ELISA). Seventeen out of the 30 clones shared the amino acid motif AFDWTFVPSLIL. The motif-containing phages and synthetic peptide AFDWTFVPSLIL blocked the binding of mAb 2D7 to CHO/CCR5 cells and competitively inhibited the ability of chemokine regulated on activation normal T cell expressed and secreted (RANTES) binding to CHO/CCR5 cells. Furthermore, the peptide AFDWTFVPSLIL also inhibited RANTES induced increase in the intracellular Ca2+ level in CHO/CCR5 cells. These results suggest that the peptide AFDWTFVPSLIL was specific for CCR5 and that it might become a CCR5 antagonist.