The study aimed to evaluate the influence of hot and cold seasons on the blood variables of Phan Rang sheep in Hue, Vietnam. The experiment was conducted on 24 sheep (01 to 36 months old). The results showed the number of red blood cells ranged from 6.58 - 7.79 million/mm3 (hot) and 7.24 - 8.82 million/mm3 (cold); haemoglobin, 7.04 - 8.64% and 8.23 - 9.67%; white blood cells, 7.60 - 8.71 thousand/mm3 and 8.00 - 9.06 thousand/mm3, P < 0.05, respectively. The hematocrit index ranged from 37.34 - 47.57% and 40.24 - 41.69%, with no significant difference between the two seasons, P > 0.05. The sheep were raised in high temperatures and humidity, the blood composition, RDW increased, mean platelet volume (MPV) and haemoglobin reduced (Hb - and MCH, respectively). MCH indicate the average, and MCHC shows the average haemoglobin weight based on red blood cell volume; MCH and MCHC were connected to breathing, ordinary respiration measurements for sheep, 25 up to 30 breaths/minute. When the temperature increased to 39 – 40°C, the respiratory frequencies reached 35 – 38 breaths/minute, depending on the temperature change over 35oC and the breathing rate increased