Laboratory bioassays were conducted to evaluate the efficacy of thiamethoxam as a grain protectant against Sitophilus oryzae, Tribolium confusum and Rhyzopertha dominica adults. Five concentrations (0.1, 0.5, 1, 2, and 4 ppm) and four commodities (wheat, maize, rice, and barley) were evaluated. Mortality rates were recorded after 7, 14, and 21 d and progeny production was assessed 65 d after exposure. Thiamethoxam was more effective at higher concentrations and S. oryzae was the most susceptible species. Surprisingly, the highest progeny production was recorded for S. oryzae with 154.3 adults/vial, while no progeny production was observed for T. confusum at 2 and 4 ppm in most of the commodities tested. To conclude, thiamethoxam can provide an adequate level of control against major stored-product insect species in wheat, maize, rice and barley.