Two trials (winter and summer) were conducted to determine certain physiological effects of water restriction on Barki sheep (to 50 or 25% of their requirements). The traits concerned were, live body weight (LBW), thermoregulatory, hematological and biochemical responses. The study was carried out at Maryout Research Station of the DesertResearchCenter, 35 km southwest of Alexandria, Egypt. A total number of 27 Barki rams aged 12-18 months were used in this study:  (1) 92-d trial, on 15 rams (averaged 40.87 ± 1.341Kg) during winter and (2) 77-d trial, on 12 rams (averaged 36.65±1.440 Kg) during summer.  Rectal temperature (RT, ºC) and respiration rate (RR, rpm) behaved similar trends as they decreased significantly (p < 0.01) as water restriction proceeded. Water restricted animals revealed significant reduction (P<0.01) in live body weight during both two seasons. Hemoglobin concentration (Hb,g/dl); hematocrit (Ht,%) and erythrocyte (RBC's) count showed similar trends in which they increased significantly (p < 0.01) as water stress proceeded while, leukocyte (WBC's)  count remained constant by water restriction in both seasons. Water stress caused significant increases (P<0.01) in blood total proteins (TP) concentration during both seasons. This increase was attributed to the increase in globulin (G) concentration (P<0.01) in winter and to the increase in albumin (A) concentration (P<0.01) in summer. Plasma cholesterol (CHO), creatinine (CRE) and alanine aminotransferase (ALT) activity were fluctuated among treated groups in both seasons. Plasma aspartate aminotransferase (AST) increased (P<0.01) in treated groups compared to the control in both seasons.