Objectives: osteoarthritis (OA) is one of the harmful disorders affecting the body joint including the temporomandibular joint (TMJ). Although OA is believed to be non-inflammatory disorder, antiinflammatory agents, as simvastatin, have been used for OA treatment. Simvastatin is presumed to possess antiosteoarthritic effect beside its antilipidemic influences. The present study tried to estimate the effect of simvastatin on the monoiodoacetate (MIA)-induced TMJ osteoarthritis. Materials and methods: thirty young adult female Sprague-Dawley rats were randomly categorized into; control, osteoarthritis and osteoarthritis with simvastatin groups. Both MIA for osteoarthritis induction and simvastatin for therapy were delivered unilaterally via the intra-articular route at the right side as a single dose for each. Results: the simvastatin administration has relatively reduced the MIA-induced osteoarthritic manifestations, and/or inhibited the progress of some osteoarthritic degenerative features but it failed to control others. The most striking findings with simvastatin administration were the prominent thickening of the condylar proliferative layer, as well as the development of osteophytes at the anterior pole of mandibular condyle. The condylar cartilage matrix showed enhancement of the extracellular matrix production with simvastatin administration. Discussion: the present study has clarified the relative antiosteoarthritic effect of simvastatin intraarticular injection. Though simvastatin has valuable palliative effect, it failed to prevent the advancement of some osteoarthritic manifestations. Conclusion: temporomandibular joint osteoarthritis (TMJOA) treated by simvastatin relieve some osteoarthritic features and modulate the structure of some joint components to compensate the damaged induced structures with MIA.