Background: The present experiment was conducted to investigate the effect of heat stress (HS) and hawthorn (Crataegus oxyacantha) fruit extract (HFE) on performance, carcass characteristics and serum parameters in broiler chickens. Methods: Experimental treatments included two different ambient temperatures (24°C: thermoneutral conditions, or 35°C: HS conditions) and three different HFE (0, 0.2 and 0.4 ml/L) in a 2´3 factorial arrangement. A total of 300 1-day-old broiler chicks were randomly allotted 1 of 6 treatments with five replicates. A total of 300 1-day old broiler chicks were randomly allocated to 6 groups with five replications of 10 birds each. HFE supplementation had no effect on growth performance, carcass characteristics and visceral weight in stressed groups (P greater than 0.05). It was also determined that it has a lowering effect on serum malondialdehyde (MDA), free fatty acid (FFA), triacylglyceride (TAG), total lipid (TL) and low density lipoproteins (LDL) (P less than 0.05), but it has no effect on other parameters (P greater than 0.05). Result: As a result, it is thought that the addition of HFE to the drinking water of broiler chickens exposed to HS has no effect on the performance characteristics, HFE has a hypolipidemic effect and would be beneficial in order to strengthen the immune system.