The present study aims to evaluate effectiveness the modified atmospheres of larvae and adults of the saw-toothed grain beetle, Oryzaephilus surinamensis based on either high carbon dioxide (CO₂) contents or high nitrogen (N₂) contents at optimum conditions (25°C and 65±5 % RH). The experiments were carried out using 20, 40, and 50% CO₂ as well as 97 and 98% N₂ gases in the air at different exposure periods. The mortality was recorded at exposure periods; 3, 6, 12, 24, 48, 72, 96, 120 and 144 h. Results showed that the larvae and adults mortalities of O. surinamensis responded to modified atmospheres (MAs) enriched with either CO₂ or N₂ and increased significantly (P < 0.01) with increasing either exposure time length or gas concentration. MAs enriched with N₂ were more effective than those contained CO_2. Modified atmospheres tested had strong effects against all stages of O. surinamensis. Six days were adequate to kill larvae and adults completely under all tested modified atmospheres contained different concentrations of CO₂. Five days were required to kill larvae were required completely under the two modified atmospheres contained 97 and 98% N₂ whereas 72 h to kill adults under the same concentrations.