Tacrolimus(FK506)is an immunosuppressive agent which is usually applied to patients who received allotransplantation to reduce immune rejection.The strong hydrophobicity of FK506 makes it difficult to be applied in aqueous system.It has been studied to be encapsulated by micelles.However,the low rate of encapsulation in micelle is an obstacle for further application.Polypeptide thermosensitive hydrogel is considered as a great candidate for drug delivery because of several advantages,such as excellent biocompatibility and biodegradability,low concentration of critical gelation and sensitive response to the stimulation of temperature.In this study,we synthesized a thermo-responsive polypeptide hydrogel by copolymerizing poloxamer(PLX)and poly(L-alanine)with L-lysine segments at the both ends to form PLX-b-poly(L-alanine-lysine)(P-Lys-Ala-PLX)copolymers.Poly(L-alanine)is the hydrophobic chain of P-Lys-Ala-PLX copolymers which was designed to capture the hydrophobic agents.The result of synthesis was performed by 1H NMR and showed that P-Lys-Ala-PLX copolymers was successfully synthesized.P-Lys-Ala-PLX has a sol-gel behavior with low concentration of 3-7 wt%and has high degree of drug encapsulation.The experiment of drug release also showed that the FK506 released constantly over time.This study indicates that P-Lys-Ala-PLX is a high potential injectable material for biomedical application.