This study aimed to evaluate the influence of gonadotrophin releasing hormone (GnRH) administration to Ossimi ewes before mating on their conception, lambing and prolificacy rates, and their mean lambs' birth weights. Twenty-one (three to five years old) Ossimi ewes and five (three to four years old) rams, (58.6±4.75kg) were recruited for this study. Ewes were allocated into three groups (7 ewes each) and synchronized with two doses of prostaglandin F2 alpha (PGF2 α) 11 days apart. Ewes of the first group (35.3±5.62kg) were flushed with corn (0.5 kg/ewe/day) for two weeks before and two weeks after mating, while ewes of the second group (37.37±7.03kg) received one ml of GnRH, 24 hours after the second dose of PGF2α. Ewes of the third group (35.28±4.11kg) served as a control. Results of this study illustrated that GnRH group had higher conception (85.71%) and lambing (85.71%) rates than corn (71.43%, 71.43%) and control (42.85%, 42.85%) groups respectively. But the difference was not significant (p > 0.05). Prolificacy rate (100%) was the same for all groups (p > 0.05); there was no twin lambing in all groups. Also, the mean lambs' birth weight was non-significantly (p > 0.05) higher in GnRH (1.88 kg) than corn (1.82 kg), and control (1.87 kg) groups respectively. In conclusion, administration of GnRH to Ossimi ewes before breeding non-significantly enhanced their conception and lambing rates, and the effect on mean lambs' birth weights was very limited.