Abstract: Estrus synchronization is an important technique in embryo transfer.Several methods have been used in cow synchronization.However,previous reports showed that the efficiency of synchronization would be different due to the situation of the recipients as well as other conditions.In the present study,the effect of GnRH on estrus synchronization of cow recipients in embryo transfer was determined,and compared with that of using PGF2α method.193 hostein cows reared in the Kunming farm were randomly divided into 3 groups.Group 1,recipients were administered once 25 mg PGF2α (5 mg/mL).Group 2,cows were injected PGF2α twice,with 11 day interval between two administration,25 mg/one injection.Group 3,cows were injected GnRH (86 μg) followed by injection of 25 mg PGF2α 7 days later and a second GnRH (86 μg) administration 16 days later.Results showed that in group 3 there were more transferable recipients (60.9%) for embryo transfer compared with that in group 1 (26.5%) and in group 2 (27.8%),respectively.It seems that interval injection of GnRH/PG/GnRH is a better method of estrous synchronization.