Atremisia sieberi Besser is a widely distributed plant that grows in many areas of Iran and has strong insecticidal activity against stored product pests, so an experiment was conducted to investigate fumigant toxicity of the A. sieberi oil collected from Karaj region of Iran. The oil was applied against one to seven day old adults of three major stored product insects including: Callosobruchus maculatus (Fab.), Sitophilus oryzae (L.), and Tribollium castaneum (Herbst). The potency of fumigant toxicity of A. sieberi on C. maculatus was higher $(LC_{50}:;1.64{mu}L;per;L)$ than S. oryzae $(LC_{50}:;4.41{mu}L;per;L)$ and T. castaneum $(LC_{50}:;20.31{mu}L;per;L)$ L). The relationships between the time exposure and oil concentration on mortality show that the mortality was increased as oil concentration and exposure time was increased. The concentration of $185{mu}L$ per L and exposure time of 24h was enough to obtain 100% kill of the insects. It was also found that the regions where A. sieberi grows affect essential oil components of the plant and can play an important role in properties of fumigant toxicity.