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This study aimed to evaluate the effect of diets supplementing with various levels of thymol and carvacrol eutectic (TCE) on growth performance, serum biochemical parameters, intestinal morphology, and the expression of intestinal nutrient absorption, barrier function- and inflammation-related genes in broiler chickens. A total of 640 one-day-old Arbor Acres male broilers with similar body weights were randomly divided into four groups (8 replicates/group, 20 broilers/replicate). Birds in the four experimental groups were fed a basal diet with TCE at 0, 30, 60, or 120 mg/kg. The results showed that the growth performance of birds during 22–42 d or 1–42 d, serum IgE and IgG content at 21 d of age, jejunal and ileal morphology, ileal <i>MUC2</i>, <i>OCLN</i>, and <i>IL-10</i> mRNA expression were significantly increased compared with the control group (<i>p</i> < 0.05), and the ileal <i>IL-6</i> mRNA expression quadratically decreased (<i>p</i> < 0.05) with increasing dietary TCE supplemented dosage, and its expression showed a linear downward trend (0.05 < <i>p</i> < 0.1). Meanwhile, compared with the other three groups, birds fed diets with 30 mg/kg TCE presented better (<i>p</i> < 0.05) growth performance, intestinal morphology, and function. These results indicated that the optimal supplementation amount of TCE in the broiler diets was 30 mg/kg.