Effects of protected fat supplementation (PF) on thermoregulatory, haematological and metabolic responses of growing Friesian calves exposed to solar radiation (SR) or kept under semi-open shed (SH) were studied through four experimental phases. The 1^st phase was to exposing the animals toSR for 6 h daily (SR). The 2^nd phase was to keep the calves under shed (SH). The 3^rd and the 4^th phases were to feeding the exposed and shaded calves on PF (SR+PF and SH+PF, respectively).  Results showed that all calves exposed to very sever heat stress at most of the day times during all experimental phases. In calves exposed to SR, temperatures of hair (HT), skin (ST) and rectum (RT), and respiration (RR) and pulse rate (PR) significantly increased by about 2.3, 4.1, 2.2, 14.5 and 4.4%, respectively. However, red blood cell count (RBC), packed cell volume (PCV%) and concentration of haemoglobin (Hb), total protein (TP), globulin  (GL), total lipids (TL), cholesterol (CL) and glucose significantly (P<0.01) decreased by about 10.1, 10.1, 4.5, 3.3 , 6.9 4.0, 4.0 and 6.0%, respectively as compared to the shaded calves. Feeding calves on PF diet led to increasing (P<0.01) all values of the thermoregulatory responses, improving RBC, PCV% and concentration of Hb, TL and CL and decreasing glucose concentration as compared to those without PF supplementation. Yet, rumen temperature, blood pH value, white blood cell count (WBC) and albumin (AL) was not affected by SR treatment or PF supplementation. On the other hand, values of RBC, Hb, TP, GL and CL during SR + PF did not differ significantly than during SH. While, values of PCV% and glucose concentration were lower (P<0.01) and of TL was higher (P<0.01) in calves during SR + PF than SH. Only, concentration of TL increased (P<0.01) in calves during SH + PF than SH. The present study suggests the possibility of using PF as a technique for ameliorating heat load on Friesian calves to improve their productivity during summer specially those exposed to solar radiation.