Fumigant activities for four essential oils; Garlic oil (Allium sativumL); Basil oil(Ocimum basilicum); Pine (Pinus longifolia L.) and Eucalyptus (Eucalyptus oblique L.) at different concentrations after 1, 2, 3, 5 and 7 days at 28±1° C were tested against 4th instar larvae and adults of the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) in the laboratory. The results showed that mortality increased with increasing oil concentration and time of exposure, also the higher essential oils toxicity at the LC50 after 7 days post-treatment was Garlic oil. Effects of Garlic essential oils on some enzymes activity in 4th instars’ larvae of T. castaneum were investigated. From this study, we conclude that these essential oils have a potential for applications in IPM programs for stored-grain pests because of its high volatility and fumigant activity.