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 (24degree celsius: thermoneutral conditions, or 35degree celsius: HS conditions) and three different HFE (0, 0.2 and 0.4 ml/L) in a 2x3 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>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<0.05), but it has no effect on other parameters (P>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.