In the present study, the effects of ginger (Zingiber officinale) on stress, antioxidant, humoral immune and cytokine responses of common carp (Cyprinus carpio) under high stocking density were investigated. The fish were assigned into four experimental groups: LD (the fish reared at 10 g L−1 and fed with the control diet), HD (the fish reared at 20 g L−1 and fed with the control diet), HD-5 (the fish reared at 20 g L−1 and fed with the control diet supplemented with 5 g kg−1 ginger), and HD-10 (the fish reared at 20 g L−1 and fed with the control diet supplemented with 10 g kg−1 ginger). After 60 days of rearing, the fish at the HD treatment exhibited significantly lower growth performance compared to the LD treatment, but the fish fed the diet supplemented with 10 g kg−1 (HD-10) showed growth performance comparable to the LD treatment. Under high stocking density, the fish had significantly higher cortisol and glucose levels, but ginger mitigated the stress responses. Plasma superoxide dismutase and glutathione peroxidase exhibited higher activities in HD, HD-5, and HD-10 treatments compared to the LD treatment. However, plasma catalase activity increased only in HD treatment. The increase in stocking density significantly increased plasma malondialdehyde levels, and ginger treatments significantly mitigated such increases. The fish at the HD treatment had significantly lower plasma lysozyme, complement and bactericidal (against Aeromonas hydrophila) activities and total immunoglobulin levels compared to those at the LD treatment; however, the dietary ginger administration inhibited these effects especially with fish fed 10 g ginger per kg diet. The fish at the HD treatment had significantly lower expression of tumor necrosis alpha (tnfa), interleukin 1 beta (il1b), and interleukin 8 (il8), and higher interleukin 10 (il10) genes. Ginger treatment, particularly at 10 g kg−1 level significantly mitigated the effects of high stocking density on the cytokines. In conclusion, the present study demonstrated that ginger treatment at 10 g kg−1 level is beneficial to suppress stress, oxidative stress, and immunosuppression caused by high stocking density in common carp. © 2019 Elsevier B.V.