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 4^th 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 4^th 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.