Objective: To show the effects of corticosteroids on inflammatory reactions in the injured Achilles tendon in rats.Material and Method: Thirty-two adult Wistar Albino rats were used in the study. The rats were divided into 4 groups. In the first group (Intact Saline), saline solution was injected to the intact Achilles tendon. In the second group (Intact Corticosteroid), corticosteroid was injected to the intact tendon. In the third group (Injured Saline), saline solution was injected to the injured Achilles tendon. In the fourth group (Injured Corticosteroid), corticosteroid was injected to the injured tendon. All groups were sacrificed on day 30 and Achilles tendons were taken and prepared for histological and biomechanical evaluation.Results: According to the biomechanical test; mean load-to-failure of the Intact Saline group was significantly lower than the Intact Corticosteroid (p=0.016), Injured Saline (p=0.001) and Injured Corticosteroid) (p=0.012) groups. According to the histopathological evaluation, tenocyte mean of the Intact Saline group was statistically lower than the Injured Saline and Injured Corticosteroid groups. Tenocyte mean of the Intact Corticosteroid group was statistically significantly lower than the Injured Saline and Injured Corticosteroid groups. The ground substance mean of the Intact Saline group was significantly lower than the Injured Saline and Injured Corticosteroid groups. The ground substance mean of the Intact Corticosteroid group was significantly lower than the Injured Saline and Injured Corticosteroid groups. There was no statistically significant difference between the groups in terms of calcification. Conclusion:It has been found that there is biomechanical and histopathological significant benefit of intra-tendon corticosteroid administration in the experimentally generated Achilles tendon injury model.