This study investigated the effects of supplementing broiler chicks’ diets with wormwood (Artemisia absinthium) oil (WO) on growth, immune function, digestion, and gut microbiota. A total of 300 unsexed Arbor Acre chicks were randomly allocated into five groups, each consisting of five replicates with 12 birds per replicate. The control group received a basal diet without additives, while WO was gradually incorporated into the basal diets of the other four groups at concentrations of 100, 200, 300, and 400 ppm. Compared to the control, the inclusion of WO at 200 and 300 ppm significantly improved live body weight, body weight gain, feed consumption, and feed conversion ratio. Additionally, at WO concentrations of 400 and 200 ppm, there was a significant reduction in uric acid and creatinine (P<0.002). Birds fed 400 ppm WO also exhibited reduced lactate dehydrogenase (LDH) levels and improved lipid profiles. Furthermore, 400 and 300 ppm WO diets resulted in significantly lower aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels, respectively. Supplementing the diet with WO at all levels enhanced digestive enzyme activities (amylase, lipase, protease, and trypsin) and antioxidant levels, including superoxide dismutase (SOD) and malondialdehyde (MDA) (P<0.001). The 300 and 400 ppm WO treatments also led to significantly increased thymus and spleen weights. Chicks fed 400 ppm WO showed the lowest levels of Escherichia coli and coliforms, while Lactobacillus concentrations were significantly higher in chicks fed diets containing 300 ppm/kg WO (P<0.001). In conclusion, supplementation of broiler diets with 300 ppm/kg WO enhances growth and immune function.