[Objectives]  Neonicotinoid pesticides are now the most widely used pesticides in the world. Studies indicate that sublethal doses of these pesticides affect the foraging, learning, and memory, of honey bees. This study investigated the sublethal effects of thiamethoxam on immune related gene expression in honey bees (Apis mellifera L.). [Methods]  (1) The LC₅₀ of thiamethoxam to honey bees was determined using the “oral-feeding tube” method；(2) The expression levels of 5 immune related genes: Abaecin (ABA), Hymenoptaecin (HYM), Defensin (DEF), Glucose dehydrogenase (GLD), and Lysozyme (LYS), and the survival of honey bees, were measured after bees had been fed sublethal concentrations (100, 10 and 2.2 μg·kg^-1) of thiamethoxam over ten days. [Results]  (1) the LC₅₀ value of thiamethoxam was 692 μg·kg^-1; (2) There were no significant differences in the expression levels of ABA, DEF and LYS relative to the control, but expression levels of HYM were significantly (P<0.01), and strongly, inhibited by sublethal concentrations of thiamethoxam, and GLD was significantly (P<0.05) up-regulated by 100 μg·kg^-1 thiamethoxam. [Conclusion]  The results suggest that sublethal concentrations of thiamethoxam can suppress HYM expression. These results are important for exploring the effects of neonicotinoid pesticides on honeybee survival and health at the molecular level.