The effect of body condition score and body weight of Sanjabi ewes on immune system, productive and reproductive performance Total 80 Sanjabi ewes (2-5 years old and 50-85 weight domain) were selected in animal unit of Mehregan farm. The ewes were divided to 4 treatment groups according to body condition score of (2, 2.5, 3, 3.5 ≤). Blood samples were collected from non-pregnant ewes, then after mating, two weeks before expected lambing and at lambing day. Blood samples of newborn lambs were also taken from the jugular vein at birth and 7 days of age. The reproductive parameters such as number of lambs born per lambing, kg of lambs born per ewes mating, pregnancy period and lamb birth weight were determined. Some blood metabolites such as glucose, total protein, albumin and globulin were determined. The white blood cell and differential leukocyte counts were also measured. The result of this experiment indicated that BCS = 3 had a significant effect (P < 0.05) on the kg lambs born per ewes. Ewes with BCS = 3 had a better performance in the percentage of lambs born per ewes at mating, while the lambing rate reduced in ewes with BCS of 3.5 or more. Birth weight of lambs was significantly affected by BCS of their ewes (P < 0.05). There was a significant effect of BCS on plasma FSH concentration in ewes with BCS more than 3 but no significant difference was seen in blood metabolite in this study. Colostrum productions and the lamb birth weights were affected by body condition score of ewes. The white blood cell counts, neutrophils and lymphocytes counts did not change between ewes and lambs. It is concluded that BCS had a significant effect on kg lambs born per ewes, birth weight of lambs, lambs weaning weight and colostrum productions (P < 0.05) and the score of 3 at mating time could optimize profitability of Sanjabi ewes.