Abstract: The hypothesis that arginine supplementation would increase antibodies production and concentrations of estrogen and progesterone-via stimulate Gonadotropin Releasing Hormone(GnRH)-in sheep was investigated. In experiment 1: Twelve Awassi ewes aged between 3.5-4.0 years weighing 48.0±2.5 kg were assigned randomly to four groups, to find whether the route of arginine administration would reflect different percentages of white blood cells, arginine and Immunoglobuline G (IgG) in the blood of ewes or not. Ewes in group one were fed ration supplemented with protected arginine (0.5 g kg-1 of body weight) (arginine group). Ewes in group tow were intravenous injected (IV) by arginine (IV group), whereas ewes in group three were intramuscular injected (Im group), group four was assigned as a control group. Percentages of white blood cells (Neutrophils, Monocytes and Lymphocytes) were recorded as well as concentrations of arginine and Immunoglobuline G (IgG) in blood of ewes were recorded. Percentage of neutrophils were increased (p<0.01) 6 h of treatment, whereas percentage of monocytes were increased (p<0.01) 12 h of treatment, meanwhile lymphocytes were decreased (p<0.01) 6 h of treatment. In general the increase and decrease of white blood cells were the highest in IV group, followed by arginine group, Im group, respectively in comparison with control group. Route of arginine administration affected the concentration of arginine in ewes blood. Levels of arginine were the highest in IV group (1697.67±945.25 mmol L-1), followed by Im group (687.33±102.71 mmol L-1), arginine group (335.00 ±17.90 mmol L-1), respectively in comparison with control group (293.33±42.48 mmol L-1). There were no significant differences between groups in IgG concentrations. In experiment 11: Twelve Awassi ewes aged between 3.5-4.0 years weighing 53.30±3.3 kg were used to find if that arginine supplementation would increase ovulation rate and concentrations of estrogen and progesterone. Experimental ewes were synchronized using intravaginal progestagen sponges. On day of sponges removal, ewes were divided into two groups. Ewes in group one were fed ration supplemented with protected arginine (0.5 g kg-1 of body weight) for 15 days; the second group was assigned as a control group. Concentrations of estrogen and progesterone in ewes blood beside the number of corpora lutea were recorded. Results showed that treatment with arginine increased the number of corpora lutea (2.38±0.67) in comparison with control group (1.00±0.58) which lead to increase lambing and twinning rate. Although of estrogen concentrations were fluctuated, but it was higher (5.92±0.33 pg mL-1) in arginine group than control group (4.56±1.06 pg mL-1). On the other hand progesterone concentrations were higher (p<0.01) (4.21±0.83 ng mL-1) in arginine group in comparison with control group (1.79±0.31 ng mL-1).