The aim of this study was to examine the impact of feeding ajwain and fennel essences on insulin resistance improvement caused by dexamethasone injection in rats as a mammalian model. For this purpose 30 mature males Wistar rats were allocated to 5 treatments and 6 replicate each in a completely randomized design. The experimental groups were consisted of: 1- Control group (no dexamethasone injection), 2- Stress group (daily injection of dexamethasone), 3- Fennel group (daily injection of dexamethasone + feeding fennel essence), 4- Ajwain group (daily injection of dexamethasone + feeding ajwain essence) and 5- Fennel + Ajwain group (daily injection of dexamethasone + feeding fennel and ajwain essences). Daily injection of dexamethasone (1 mg/kg body weight) into the thigh muscle was performed to create stress condition. Fennel and ajwain essences and their mixture (50:50) were fed (100 mg/kg of body weight of rats) for 27 days through gavage. The results showed that fennel and ajwain essences had lower antioxidant capacity than BHT based the IC50 index. The stress condition caused pancreatic weight loss (P 0.05), however consuption fennel essence and the mixture of fennel and ajwain essences partially improved weight loss. The testicles weight increased (P 0.05) in tress group and there was no difference between the control and other groups that consumed the essences. The area of Langerhans islands was not affected by the experimental treatments. The highest and lowest glucose level (P 0.05) was observed in the stress group and the ajwain group, respectively. Feeding the mixture of fennel and ajwain essences increased (P 0.05) concentration of insulin hormone compared to the control, stress and fennel groups. Superoxide dismutase enzyme and total antioxidant capacity were affected (P 0.05) by experimental treatments, in such a way that the maximum level of superoxide dismutase activity belonged to the control group and the minimum level was observed in stress group. Moreover, superoxide dismutase activity was significantly higher (P 0.05) in essesnce groups than the stress group. Total antioxidant capacity in control group was higher (P 0.05) than the fennel group and the other groups were intermediate in this respect. In conclusion, dexamethasone injection caused incidence of diabetes and disruption of pancreatic beta cells activity through the induction a stress condition in rats. Consuming some herbal essences (especially ajwain and the mixture of awain and fennel essences) improved this condition because the antioxidant effects. Keywords: Dexamethasone, Oxidative stress, Fennel essence, Ajwain essence, Blood metabolites, Histology