Thiamethoxam (THM), a neonicotinoid insecticide, controls various insect pests that attack fruits, vegetables, and field crops. However, improper handling and prolonged exposure to thiamethoxam can lead to adverse health effects. The objective of this study was to eliminate the toxic effects of THM in liver, kidney and brain of male rats by incorporating vitamin C into their diets. Rats were divided into six groups (8 males per group): the control group (which supplied distilled water orally), the vitamin C group (which injected 200 mg/kg BW of vitamin C), three THM groups received two graded levels as follows, 1/10 LD₅₀ (156.3) and 1/20 LD₅₀ (78.15) mg/kg BW orally. The results showed that exposure to THM at the two levels (1/10 and 1/20) reduces food intake, which reduces body weight gain, as well as carcass weights. It also reduces red blood cells and hemoglobin. It raises blood glucose and liver enzymes (ALT, AST, and ALP), as well as MDA, which indicates a high level of oxidative stress leading to decrease in immune-markers (IgM and IgA). Therefore, adding vitamin C in the rats' diet reflects all the above-mentioned parameters near to the control levels. The simultaneous application of vitamin C along with THM eliminated the harmful impacts of the pesticide on the enzymatic and non-enzymatic antioxidant system, enhancing the liver, kidney, and immunoglobulin markers. The side effects of THM were also confirmed in histopathological examinations, where major alterations in liver, kidney, and brain tissues’ structure were recorded. It concluded that vitamin C can mitigate adverse effects of the THM toxicity in non-target species.