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Using a mouse exo utero system to examine the effects of fetal jaw movement on the development of condylar cartilage, we assessed the effects of restraint of the animals' mouths from opening, by suture, at embryonic day (E)15.5. We hypothesized that pre-natal jaw movement is an important mechanical factor in endochondral bone formation of the mandibular condyle. Condylar cartilage was reduced in size, and the bone-cartilage margin was ill-defined in the sutured group at E18.5. Volume, total number of cells, and number of 5-bromo-2'-deoxyuridine-positive cells in the mesenchymal zone were lower in the sutured group than in the non-sutured group at E16.5 and E18.5. Hypertrophic chondrocytes were larger, whereas fewer apoptotic chondrocytes and osteoclasts were observed in the hypertrophic zone in the sutured group at E18.5. Analysis of our data revealed that restricted fetal TMJ movement influences the process of endochondral bone formation of condylar cartilage.