The greatest challenges facing dairy farmers is heat stress. The summer season in Egypt is relatively long. This experiment aimed to study the effect of summer heat stress on some haemato-biochemical parameters and the growth performance of suckling Friesian calves. Eighteen Friesian calves with an average body weight of 30±1.5 kg were used and assigned into two groups (n= 9). The calves in the first group were reared inside an open pen without fans or sprinkling water. While the calves in the second group were reared in a well-ventilated fans pen as well as, the calves were sprinkled with water daily from 10 a.m. to 2 p.m. The results revealed that feed intake and body weight gain were significantly (P<0.05) decreased while water intake was increased by heat stress (HS). Also, parameters such as rectal or core body temperature (RT), respiratory rate (RR) and pulse rate (PR) are increased significantly. The levels of serum total protein and glucose decreased. Moreover, haemoglobin (HB) level, red blood cells (RBC), and total leukocytic (WBC) counts were significantly reduced in heat-stressed calves. It is concluded that keeping calves in a hot environment leads to a series of metabolic and physiological changes to reduce this stress.