Temporomandibular joint and muscle disorders are a group of conditions that cause pain and dysfunction in the jaw joint and the muscles that control jaw movement. Intra-articular injections are one of the methods that physicians may use to treat joint pain. Corticosteroids were the first substances to be injected commonly into the intra-articular space; corticosteroids were found to lower indicators of the inflammatory response. The indications and effectiveness of intra-articular steroid injections have been debated since their introduction. This study conducted on 36 rats whom injected by Depo-Medrol in the temporomandibular joint which is normally functioning 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; so the groups and the sub-groups are: Group A: A1, A2 -Group B: B1, B2 -Group C: C1, C2 All rats of the group A were injected one time, A1 were sacrificed after (1) week from injection; A2 were sacrificed after (2) weeks from injection. All rats of the group B were injected two times at (0, 6) weeks, B1 were sacrificed after (1) week from last injection, B2 were sacrificed after (2) weeks from last injection. All rats of the group C were injected three times at (0, 6, and 12) weeks, C1 were sacrificed after (1) week from last injection; C2 were sacrificed after (2) weeks from last injection. All the specimens examined histological by light microscope after staining with Haematoxlin and Eosin; which showed affection of bone trabeculae and widening of marrow spaces in both the condylar head and temporal bone, the content of marrow spaces filled with fibrous tissues and no inflammatory cells in the beginning of injection but with more injections signs of inflammatory invasion and fatty degeneration appeared and presence of reversal line which represent new bone formation, no bone resorption, no changes in the disc and retrodiscal tissues.