Blood samples were collected from the jugular vein of 101 clinically healthy Iranian fat-tailed sheep according to their age (<1, 1-3, 3-5 and >5 years) and sex. Serum haptoglobin (Hp) was measured based upon the preservation of the peroxidase activity of haemoglobin, which is directly proportional to the amount of Hp. The reference value for serum Hp of apparently healthy Iranian fat-tailed sheep was 0.05-0.18 g/l. Age and sex had no significant effect on the serum concentration of Hp in examined animals.