The use of carbon dioxide (CO2) is a very effective method for controlling insect pests. The effects of CO2 on developmental stages of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) and Trichogramma embryophagum Hartig (Hymenoptera: Trichogrammatidae) were determined in this study. We aimed to establish a technique that can be used for controlling the stored-product pest, E. kuehniella with a natural enemy, T. embryophagum. Egg, larva, pupa and adult stages of E. kuehniella and T. embryophagum were exposed to 0, 10 and 20% CO2 gases in a CO2 incubator at 27 degrees C and atmospheric pressure for different exposure times. The adult stage of E. kuehniella was more sensitive than its egg, larva and pupa in either percentage of CO2 or increasing exposure time. But the adult of T. embryophagum was the most sensitive stage at only highest dose of CO2. On the other hand the larvae of T. embryophagum were the most resistant stage at 10% CO2. Consequently, the developmental stages of two insect species had different susceptibility to increasing percentage of CO2. These results suggest that a low percentage of CO2 may be used with T. embryophagum for controlling the stored-product pest, E. kuehniella.