The objective of this study is investigating the effects of Lonicerae flos extract (LFE) on antioxidant status, intestinal development, and jejunum barrier function in heat-stressed broilers. Two hundred and forty male broilers (28-day-old) were assigned to normal control group (NOR, 22°C, basal diet), heat stress group (HS, 32°C, basal diet) and Lonicerae flos extract supplementation group (LFE, 32°C, basal diet with 400 mg/kg, 800 mg/kg, 1200 mg/kg LFE). Results indicated that Heat stress significantly impaired growth performance, increased serum aspartate aminotransferase (AST) and d-lactate levels, decreased jejunal mucosal total antioxidant capacity (T-AOC) and jejunal villus height (P < 0.05) throughout the entire experimental period. Although not statistically significant for growth performance, Lonicerae flos extract numerically reduced the feed-to-gain ratio by 8.5 % after 14 days. Lonicerae flos extract, particularly at 800 mg/kg, significantly mitigated the heat stress-induced elevation in serum AST and d-lactate levels and enhanced jejunal T-AOC and superoxide dismutase (SOD) activity and jejunal villus height (P < 0.05). Lonicerae flos extract activated Nrf-2 pathway, downregulated the mRNA expressions of endoplasmic reticulum stress (ERS) and apoptosis-related genes, and enhanced the mRNA expressions of tight junction proteins in jejunum mucosa of heat stressed-broilers. The 800 mg/kg dose was identified as the most effective. In conclusion, dietary LFE effectively improved intestinal integrity and antioxidant capacity in heat-stressed broiler through activating Nrf-2 pathway, alleviating ERS-dependent apoptosis and improving jejunum barrier function.