aim   of  the  study:  to  evaluate  the  short  term  effect  of  corticosteroid  injection  on temporomandibular joint structure. materials and methods: Thirty six adult rats with weight ranged between 150-200 gm were included in the current study with normally functioning temporomandibular joint. The rats were divided into three groups: A, B, and C. every group is divided into (2) sub-groups. Each sub- group had (6) rats. All rats of the group A were injected one time, A1  sacrificed after one week, A2 sacrificed after 2 weeks form injection. all rats of the group B were injected 2 times at (0&6 weeks), B1 sacrificed after one week from last injection, B2 sacrificed after 2 weeks form last injection. . all rats of the group C were injected 3 times at (0,6&12 weeks), C1 sacrificed after one week from last injection, C2 sacrificed after 2 weeks form last injection. Results: injection of corticosteroids for the 3rd time showed signs of inflammatory invasion and fatty degeneration showed in all cases.