Abstract: Two experiments were conducted to investigate the ability of leptin to mediate the effects of energy on the gonadotrophins secretion. In the first experiment, twenty-eight cyclic Chal ewes were assigned randomly to dietary energy restricted (60% of maintenance; n = 14) and control (100% of maintenance; n = 14) groups for 71 days (6 estrous cycles). Estrus was synchronized with seven consecutive injections of PGF2a. Biweekly, Body Weight (BW) and Body Condition Score (BCS) were determined and blood samples were collected to measure plasma leptin concentration. Blood samples were also taken to determine plasma progesterone concentration twice weekly. After each PG injection and from second injection to the end of experiment, four ewes were selected and blood samples were collected at 20 min and hourly intervals for 3 h to detect plasma LH and FSH concentration. In the 2nd experiment, after the ceasing of estrous cycle caused by energy restriction, six acyclic ewes were selected and randomly alloted to two groups (n = 3) and received the following treatment for four days. All ewes in group I were fed with a ration which provided 60% of maintenance energy requirements and intravenously injected with 4 μg leptin kg-1 BW in every day. All ewes in group II were fed with a ration that provided 180% (120+60%) of maintenance energy requirements and intravenously injected with 1 mL saline in every day. In both groups, blood samples were collected at 20 min and hourly intervals for 3 h before feeding on day 0 and day 5 and for 3 h before and after injections as above on day 2 and day 4 to detect plasma LH and FSH concentration. In the first experiment, BW and BCS from the second estrous cycle and leptin from the third estrous cycle to end of experiment significantly (p<0.05) decreased. In the dietary energy restricted ewes, mean plasma concentrations of FSH significantly (p<0.01) decreased from fourth estrous cycle to day 71 and LH pulsatile secretion suppressed on day 71, so that, mean plasma concentrations of LH (p<0.05) and LH pulse frequency (p<0.01) and LH pulse amplitude (p<0.05) significantly decreased. In the second experiment, injection of leptin significantly increased mean circulating concentrations of LH (p<0.05), LH pulse frequency (p<0.01) and LH pulse amplitude (p<0.05) and mean circulating concentrations of FSH (p<0.01) and leptin (p<0.01). High energy intake significantly (p<0.05) stimulated pulsatile secretion of LH and leptin secretion (p<0.01), but increased non-significantly plasma FSH concentration. The results of this study imply that the effects of energy on the gonadotrophins secretion are mediated by leptin in ewe.