Some physiological and haematological parameters were measured in 80 horses in Thanh Tri district, Ha Noi city. The horses belonged to 4 different age groups. The studied results showed that horse body temperature (rectal temperature) ranged from 37.4°C to 39°C. The heart rate and respiratory frequency were highest in the horses at the age of under 2 months, then gradually decreased in the other older age groups
lowest in the horse group of 4 - 8 years old. A number of red blood cells and blood cell density decreased by the age groups
highest in the horse group under 2 months old and lowest in the horse group of 4 - 8 years old. The mean red blood cell volume increased by the age groups, percentage of blood cell volume in the female breeder were lower than that of the other age groups. The mean corpuscular hemoglobin volume of the white horse decreased by the age groups, whereas
mean corpuscular hemoglobin concentration in one red blood cell increased by the age groups. A number of white blood cells were highest in the white horses at the age of around 1 year, neutral white blood cells accounted for highest rate in the horses under 2 months old and from 4 to 8 years old while lymphocytes reached the highest percentage value in all kinds of white blood cells in post-weaning horses at the age of 1 to 2.5 years... Number of platelet was fluctuated in a range of 148 to 501 thousand/mm3 and mean platelet volume was in a range of 7.61 - 8.06 fl. Mean diameters of erythrocytes, eosinophils, basophils, neutrophils, monocytes, large lymphocytes and small lymphocytes were 5.7 um, 12.4 um. 12.2 um, 11.7 um. 14.9 um, 10.8 um. and 6.9 um, respectively.