Aims: To investigate the expression of aromatase in temporomandibular joints(TMJs) of male and female rats of different ages. Methods: The expression of aromatase in terms of protein and mRNA was examined by immunohistochemistry, Western blot, and in situ hybridization in the TMJs of Sprague-Dawley rats. The expression level of aromatase protein was also quantified by the density of aromatase-positive chondrocytes in TMJ condylar cartilage. A tritiated water assay was used to analyze the activity of aromatase in cartilage chondrocytes. Results: Strong aromatase protein and mRNA hybridization signals were detected in hypertrophic and mature chondrocytes in all the cases examined. The density of aromatase-positive chondrocytes was relatively stable at higher levels before 8 weeks of age. The density decreased gradually in females after 8 weeks of age but not in males. Conclusion: These results demonstrate that aromatase is expressed intensely in condylar cartilage and suggest that it may play an important role in pathophysiological mechanisms in condylar cartilage. Keywords: aromatase, cartilage, chondrocytes, estrogen, temporomandibular joint