Growth hormone releasing peptide-6(GHRP-6)plays an important role in animal growth.However,there was few study focused on the effect of GHRP-6 on animal growth through controlled-release system.We have synthesized PLGA-PEG-PLGA copolymer to investigate its control-released effect on GHRP-6 in vitro and to study the effect of GHRP-6-copolymer hydrogel on the growth of rex rabbits.The copolymer was synthesized using ring-opening copolymerization and characterized by 1H NMR.The interaction between GHRP-6 and copolymer was characterized by Fourier transform infrared(FTIR)and X-ray diffraction(XRD).The body weight,serum level of insulin-like growth factor-1(IGF-1)and hair coat quality were studied in rex rabbits.The results showed that hydrogen bonding forms between N-H group in GHRP-6 and C=O group in copolymer.The release mechanism of GHRP-6 was the combination of diffusion-controlled and erosion-controlled in the copolymer.The serum level of IGF-1,hair coat quality and body weight was both significantly higher in the GHRP-6-copolymer hydrogel group than other groups.These results indicate that the copolymer can effectively control the release of GHRP-6.In addition,the GHRP-6-copolymer hydrogel can increase the synthesis of IGF-1 for a prolonged period,thereby increasing the rex rabbits growth and hair coat quality.