In the present study, we evaluated the effects of dietary single strain or multistrain Lactococcus lactis on the intestinal health, innate immunity, and antioxidant activity of common carp. Common carp (44.79±0.13 g) were fed a control diet or one of the seven diets with supplementary Lactococcus lactis [Lactococcus lactis Q-8 (G1); L. lactis Q-9 (G2); L. lactis Z-2 (G3); L. lactis Q-8 and L. lactis Q-9 (G4); L. lactis Q-8 and L. lactis Z-2 (G5); L. lactis Q-9 and L. lactis Z-2 (G6); L. lactis Q-8, L. lactis Q-9 and L. lactis Z-2 (G7)] for 60 days. The corresponding results showed that the activities of intestinal digestive enzymes (protease, amylase, and lipase) and the expression of tight junction protein [Claudin, ZO-1] genes were significantly increased by treatment with dietary Lactococcus lactis; further, the effects of the multi-strain treatment groups were significantly higher. In addition, all treatment groups exhibited significantly higher microvilli length in the midgut and enhanced levels of tumor necrosis factor-alpha (TNF-α, except G6), interleukin-6 (IL-6), IL-12, IL-1β, IL-10 (except G7), transforming growth factor-beta (TGF-β), and nitric oxide (NO) production in the serum, compared to those of the control group. Multistrain treatment significantly increased the muscle thickness of the entire intestine; however, the effect on alkaline phosphatase (AKP) activity in the serum was not significant. Nonetheless, the regulatory effects of dietary Lactococcus lactis on the antioxidant capacity of the hepatopancreas were significantly higher than those of the control group, and the G7 group had a more prominent effect on glutathione peroxidase (GSH-Px), glutathione (GSH) and malondialdehyde (MDA) production. In conclusion, the three Lactococcus lactis strains evaluated in this study were effective in improving intestinal health, immune response, and antioxidant capacity in common carp and exhibited a synergistic effect when used as a combined dietary treatment. Overall, this study can provide an additional reference point for the application of probiotics in aquaculture.