The current study aimed to characterize the plateau patterns of plasma progesterone in the peripheral circulation during the application of vaginal sponge impregnated with different concentrations of medroxyprogesterone acetate (MAP) and co-treated without and with different doses of equine chorionic gonadotropin (eCG) and its effects on some items of reproductive performance. Determination the onset surges (time and level) of LH and estradiol-17β were also aimed in the study as a necessary pinpoint to the time of ovulation after MAP sponge-eCG treatment. Forty Barki ewes were randomly allocated into 2 main groups (A & B) of equal numbers (n=20/group). Groups A and B were treated with vaginal sponges containing 25 and 50 mg MAP, respectively. On day of sponge's withdrawal, ewes of each main group were randomly reassigned according to eCG dose into three subgroups (1, 2 and 3). Groups A1 and B1 (n=6 each group), served as control, without eCG injection, while groups A2 and B2 (n=7/subgroup) were injected at sponge removal with 300 IU/eCG, whereas, groups A3 and B3 (n=7/subgroup) were injected with 500 IU/eCG. Blood samples were taken immediately before sponge insertion and after the placement subsequently every 2 days and continued to the end of sponge application to studying the plateau pattern of progesterone in the peripheral circulation. Nine hours after sponge removal to 74h latter, blood samples were also taken every 3h and 6h for determination LH and estradiol-17β surges, respectively. The time to onset estrus (h), estrus duration, pregnancy and lambing rates (%) were recorded as reproductive performance measuring related to the study. The started level of plasma progesterone in group A increased gradually with level reaching to its maximum level on days 6 and 8 of sponge application and then rapidly decreases reaching to minimum level on day of sponge removal. On contrast, the patterns of plasma progesterone changes in group B were forcefully increased but with slightly high level from the beginning reaching its highest concentration on day 6 and day 8, then decline gradually to reach lower level on the day of sponge withdraw. The mean time from sponge withdraw to LH and estradiol-17β surges were significantly shorter (P<0.05) in-group A than B and significantly longer (P<0.01) in group A1B1 than other eCG treated groups. Neither MAP nor eCG have significant effects on LH concentration, while, eCG have positive effects on the concentration of estradiol-17β. Generally, the hormonal plateau patterns of group A were associated with acceleration the time to onset estrus with high pregnancy rate. In conclusion, the protocols used for estrus synchronization in sheep are associated with different plateau patterns of circulating reproductive hormones and subsequently affect reproductive performance.