Abstract: The toxicities of CO₂ to Stegobium paniceum were studied at concentrations of 10%, 30%, 50%, 70% and 90%. The results showed that toxicity to S. paniceum increased with the concentration of CO₂. Besides, S. paniceum adults and larvae showed different susceptibilities to the CO₂ stress. Under 10% CO₂, the LT₅₀ and LT₉₉ of adults were 22.39 h, 92.36 h, and those of larvae were 442.13 h, 1853.56 h, respectively. When treated by 90% CO₂, the LT₅₀ and LT₉₉ of adults were 6.89 h, 15.83 h, and those of larvae were 18.76 h and 60.58 h, respectively. In addition, after treatment with CO₂ concentrations, lower polysaccharides and higher soluble protein contents (except for the 90% CO₂ for protein) were detected in the dead adults than in larvae. Under 50%, 70% and 90% CO₂ concentrations, the polysaccharides contents were 7.65, 9.08 and 10.45 μg/insect in adults, and 8.12, 9.94 and 11.02 μg/insect in larvae, respectively. Under 30% and 70% CO₂ concentrations, the soluble protein contents were 127.66 and 155.98 μg/insect in adults, and 110.46 and 142.25 μg/insect in larvae, respectively. Regardless of the CO₂ concentration, polysaccharides were metabolized at a higher rate than soluble protein, although metabolism rates of both polysaccharides and protein decreased with increase in CO₂ concentration. Besides, both polysaccharides and soluble protein were metabolized at a higher rate in larvae than in adults. Under 10% CO₂, the metabolism rates of polysaccharides and protein were 68.53% and 51.02% in adults, 71.87% and 59.66% in larvae, respectively. Under 90% CO₂, the metabolism rates were 22.74% and 7.05% in adults, 33.89% and 18.07% in larvae, respectively. The results indicate that polysaccharides is the primary energy source, compared with soluble protein, in the beetle's response to CO₂ stress, and that S. paniceum larvae is more tolerant to CO₂ stress than adults.