Abstract: Plant extracts contain compounds that show antifeedant, deterrent and toxic in insects.Therefore, efficacies of essential oils from Mentha longifolia L. and Thymus kotschyanus Boissand Hohen were tested on nutritional indices and oviposition deterrence of Tribolium castaneum(Herbst). Essential oils were extracted by hydrodistillation using Clevenger type apparatus.Several experiments were designed to measure the nutritional indices such as relative growth rate(RGR), relative consumption rate (RCR), efficiency of conversion of ingested food (ECI) andfeeding deterrence index (FDI). Treatments were evaluated by the method of flour disk bioassayin dark, at 27±1°C and 65±5% R.H. Several concentrations (200, 1000, 1500, 2000, 3000 and4000ppm) were used to assess antifeedant activity of the essential oils. In this experiment, 10insects were introduced into each treated disk, and the indices were estimated three days later.Oviposition deterrence was evaluated using black filter papers impregnated with severalconcentrations of the essential oils (6000-38000ppm). Results showed that M. longifolia oil washighly effective compared with T. kotschyanus and decreased the RGR, RCR and ECIsignificantly. Moreover, M. longifolia significantly increased feeding deterrence. The plantessential oils tested reduced the oviposition rate of T. castaneum significantly. At the highestconcentration (38000 ppm) of M. longifolia and T. kotschyanus, oviposition deterrence was95.9% and 89.43%, respectively. Findings indicate the capability of these plant essential oils inthe management of T. castaneum in storage.