In recent decades, the Significant amounts of pollutants, including pesticides, have found their ways into the water resources. Deltamethrin, with the trademark “Decis EC %2.5” is used as an alternative to organophosphates in the fights for controlling pests, due to their environmental sustainability and high toxicity. The stability and durability of pesticides and insecticides in the aquatic environment cause acute and chronic poisoning in fish and other aquatic organisms. The aim of this study was to improve the immune and stress oxidative response of common carp under the influence of deltamethrin toxin following a diet containing lactoferrin. The no. of 60 fish with a mean weight of 30 + 1.64 g and a mean height of 13.5 + 1.23 cm were initially divided into 2 nutrition groups. The fish in the control (with basal diet) and lactoferrin groups were fed 400 mg / kg food for three weeks. After this period, the initial sampling as well as blood sampling were fulfilled. The results showed that there were no significant differences between the two groups in growth indices (WG, CF, SGR, FCR) and hematological indices. No significant difference was observed between the two groups after analyzing the rates of protein, albumin and CAT levels. The level of AST in lactoferrin treatment was less than that in the control group, and the amount of SOD enzyme was increased in the lactoferrin treatment. After three weeks of feeding, it was stopped and the treatments were divided in order to be exposed to deltamethrin. Moreover, the control group was divided into two control groups without deltamethrin and the control group exposed to deltamethrin. Also, the lactoferrin group was divided into two lactoferrin-free group and lactoferrin group exposed to deltamethrin. After 12 days of exposure to venom, blood samples were taken from different treatments. The hematological results showed that compared to other treatments, deltamethrin in the control treatment with basal diet reduced white blood cells and monocytes, and increased neutrophils. Lactoferrin treatment exposed deltamethrin had the highest no. of white blood cells. Based on the results, compared to the other treatments, deltamethrin in the control treatment led to increase in total protein, albumin, SOD and CAT, but lactoferrin plus deltamethrin reduced these factors to near the control treatment rates. The results also showed that deltamethrin reduced AST in the control treatment exposed to deltamethrin compared to other treatments. The results suggest that the diet containing lactoferrin is effective in enhancing antioxidant defense and reducing oxidative stress during the toxicity induced by organophosphorus pesticides. Keywords: Deltamethrin, Oxidative stress, Lactoferrin, CAT, SOD