This study aims to identify the effect of adding thiamine to the diets of pregnant ewes before and after birth. Two seasons were conducted to determine the effect of thiamin supplementation (vitamin B1) to the rations of pregnant ewes on some blood components. Feeding trial was conducted using forty pregnant ewes aged 2-4 years and averaged initial body weight of 35.0±0.05 kg /head. Ewes divided into four similar groups (5 for each) using the randomized complete block design for feeding trial. All animals of the experimental groups were fed on ration consisted of concentrate feed mixture (CFM), berseem hay (BH) and wheat straw (WS) at the ratio of 2: 1: 1 on DM basis, respectively. Control and tested treatments (T1), (T2) and (T3) were respectively supplemented by 0, 20, 30 or 45mg/day/head thiamin. Animals were fed according to NRC, (1985) standard for sheep. Blood sample were taken before lambing and monthly after lambing to determined blood components. The diets of ewes were starting to supplemented by thiamin fourteen weeks before lambing and ten weeks after lambing. Results indicated that feeding lactating ewes on 20, 30 or 45 mg/h/d of thiamin blood constituents indicated that the plasma total protein tended to be higher in group 1, 2, 3 compared with control before lambing. In addition, the data show that there was significant increase (p<0.05) in plasma total protein after lambing in the first season, in the second season the plasma total protein tended to be higher in group 2, 3 before lambing but there was significant impact (p<0.05) in group 1, 2 after lambing .Also, The group fed 30 mg thiamine showed significant increase (p<0.05) in plasma albumin before lambing in season one. Moreover, the group feed 20 mg thiamine showed significant increase (p<0.05) in plasma albumin in the first month after lambing. In addition, Plasma glucose was found to be higher with the supplementation different levels of thiamine in ewes. Moreover, in second month after lambing there was significant increase (p<0.05) in Plasma glucose concentration than control group (p<0.01). No significant difference between treatments in GOT, GPT and thyroid hormones (T3 and T4) concentration with slightly increases in its values in the thiamin treatments. It could be concluded that using thiamin as feed additive in ration formulation of pregnant ewes tended to improve productive performances and physiological responses as blood composition. The rate of 45 mg/h/d of thiamin supplements could be performed the best concerning the productive performance.