Objective  To test the differential Estrogen Receptor（ER） beta levels of mitochondrial proteome of mandibular condylar chondrocyte in the rat model of temporomandibular joints osteoarthritis（TMJOA）. Methods  25 SD rats were divided into experimental group（15 rats） and control group（10 rats） randomly. TMJOA models were created in left sides of TMJ of 15 SD rats by the partial resection of the articular disc. The experimental rats were killed 3 months after operation. After the chondrocytes culture, Immunohistochemistry, semiquantitative RT-PCR and Western blot were used to test the differential ER beta expression levels in mitochondrial proteome of mandibular condylar chondrocytes. Mitochondrial proteins identification was carried out by two-dimensional electrophoresis and peptide mass fingerprint（PMF）. Results  PMF showed that one of the differential proteins was ERβ. Immunohistoche-mistry and Western blot results suggested the significant difference of ERβ protein levels between operation-treated and control group. The operation-treated group had

lower ERβ levels（P<0.01）. Conclusion  It has been demonstrated that ERβ protein levels were decreased in mitochondria of TMJOA mandibular condylar chondrocytes, which suggests a role for mitochondrial ERβ in the effects on TMJOA. The pathological role of ERβ in the regulation of TMJOA progress remains to be elucidated.