A N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-CXCR4 antagonist (BKT140) conjugate (P-BKT140) was developed and its biological activities were tested. Both free BKT140 and monomer MA-GGPLGLAG-BKT140 (MA is methacryloyl) were prepared by solid phase synthesis. P-BKT140 was prepared by reversible addition-fragmentation chain transfer (RAFT) copolymerization of monomers HPMA and MA-GGPLGLAG-BKT140. The in vitro results show that the free BKT140 and P-BKT140 have similar cytotoxicity against human prostate carcinoma PC-3 cells, indicating that conjugation of BKT140 to HPMA did not significantly impact the cytotoxicity of BKT140. Both BKT140 and P-BKT140 inhibited the CXCL12-induced migration of PC-3 prostate cancer cells, but the P-BKT140 conjugate possessed a substantially higher inhibition activity than free BKT140.