Galleria mellonella (Linnaeus, 1758) is a Lepidopteran pest insect infesting the honeycombs, and the last instar larva of the insect is also a valuable model organism for the evaluation of drug efficacy, pathogenicity of infectious agents and environmentally sound chemical insecticides. Levamisole is an anthelmintic drug that is used for the treatment of parasitic infections in animals. In this study, we investigated the oxidative and genotoxic effects of dietary levamisole on the haemolymph of G. mellonella last instars to evaluate levamisole as an alternative chemical for traditional insecticides. In this context, first instar larvae were reared up to the last instars on artificial diets containing levamisole (w/w) and a control diet without levamisole. Malondialdehyde (MDA) and protein carbonyl (PCO) contents, and the activity of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST) and glutathione peroxidase (GPx) were determined to evaluate oxidative stress in the haemolymph of G. mellonella last instars. Furthermore, a comet assay was performed on haemolymph for evaluating DNA damage levels. The dietary levamisole led to a significant decrease in MDA and PCO contents and antioxidant enzyme activities (SOD, CAT, GST and GPx) when compared to the control diet. However, dietary levamisole significantly increased tail moment, tail %DNA and tail length, which are strong indicators of DNA damage. We infer from these that levamisole induced DNA damage and crippled antioxidant enzymatic defence in correlation with gradually increasing dietary concentration. The study would also provide valuable insights into the multifunctional aspects of levamisole, including its use in pest management.