Effects of three packing materials and exposure time on the mortality of Plodia interpunctella and Tribolium castaneum were studied using CO₂-modified atmosphere control. Materials used were triple layered craft paper (KKK), triple layered craft paper with one laminate coating layer (KLK), and triple layered craft paper with one HD film coating layer (KHK). In the test balls (ø 1.2 m) containing 85% CO₂-modified atmosphere, concentration of CO₂ in small packing envelopes (9.8×9.8 ㎝) made of the materials after one day was higher in KKK (26.67±0.58%) than KLK (23.33±0.58%) or KHK (20.67±0.58%). Both P. interpunctella and T. castaneum showed higher mortality in KKK than in either KLK or KHK. Similar results were obtained by larger space (9×4×3 m) and packing volume (20 ㎏) studies. The effect of the packing materials was clearer on T. castaneum more tolerant to CO₂ than P. interpunctella. Regression of the insect mortality on cumulative concentration time (∫<SUP>t</SUP>₀c × tdc ≈ ∑concentration × time) was highly significant. Control of P. interpunctella and T. castaneum by CO₂-modified atmosphere were discussed in relation to packing materials, cumulative concentration time of CO₂ and food products.