Four compounds (trans-anethol, thymol, eugenol and cinnamaldehyde) occurring naturally in the plant essential oils were evaluated for contact and fumigant toxicity against adult, 10 day and 18 day old larvae of Tribolium castaneum (Herbst). The insecticidal activities varied with concentration, compound and the exposure time. The most sensitive stage was 10 day old larvae followed by adult T. castaneum. Eighteen day old larvae were highly tolerant of the tested compounds. Cinnamaldehyde and eugenol were highly effective against T. castaneum when applied for highest exposure time of 48 h at the lowest dose. At the highest dose level of 0.288 mg cm-2 and lowest exposure time of 6 h, trans-anethol achieved 100% mortality of 10 day old larvae as contact toxicity, whereas highest dose level of 115.38 and 6.153 mg-1, thymol and eugenol achieved only 36.66 and 30% of 10 day old larvae and adult of T. castaneum as fumigant toxicity. Against 18 day old larvae, eugenol and cinnamaldehyde achieved 100% mortality after exposure for 48 h, even with the highest dose volume. These compounds may be suitable as contact and fumigants because of their high effectiveness and their safety.