In the present study, the effects of dietary lavender (Lavandula angustifolia) extract (LE) on growth performance and immune, antioxidant, and stress responses in common carp, Cyprinus carpio were investigated. For this, four diets containing 0, 0.5, 1.0 and 1.5% LE were offered to triplicate groups of fish (25.8 ± 1.66 g) for 70 days, and then the fish were exposed to a 3-h crowding stress. Growth performance, blood leukocyte count, plasma proteins and innate immune parameters, and head kidney cytokines’ gene expression were studied after the 70-day feeding trial (before the crowding stress). Plasma cortisol, glucose, superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA) were measured before and after the crowding stress. Results showed that dietary LE had no significant effects on the fish growth performance, blood leukocyte differential count, plasma albumin and total protein, and head kidney interferon gamma-1 gene expression. Blood leukocyte and plasma globulin, alternative complement and total immunoglobulin significantly increased in the fish fed with 1.0–1.5% LE diets compared to the fish fed with the control diet (0% LE). The plasma lysozyme activity significantly increased along with dietary LE supplemental levels. The lowest expression of interlukin-1 beta gene was related to the 1.0% LE treatment. Tumor necrosis factor-alpha gene expression significantly decreased along with increase in dietary LE levels and the lowest expression was related to the fish fed with 1.5% LE diet. The LE administration led to significant increase in interlukine-10 gene expression and the highest expression was related to the fish fed with 1.0% and 1.5% LE diets. The fish fed with 1.5% LE diet had significantly higher transforming growth factor-beta gene expression compared to the control group. Liver SOD and CAT activities showed significant increases along with dietary LE supplementation levels. After the crowding stress, hepatic SOD decreased in the control group, but not the LE-supplemented groups. Stress led to significant decrease in hepatic CAT activities in all treatments, but CAT activity increased along with the LE levels with highest activity in the fish fed with 1.5% LE. The stress led to significant increase in hepatic MDA in the treatments control and 0.5% LE, but not 1.0–1.5% LE groups. The stress led to significant increase in plasma cortisol and glucose levels in all treatments but dietary LE levels significantly decreased these parameters. Dietary LE supplementation at levels of 1.0–1.5% is recommended for common carp to suppress stress, inflammation and oxidative conditions and augment immune responses in the fish. © 2019 Elsevier B.V.