OBJECTIVE The aim of the present study was to clarify the effects of a liquid diet on the temporomandibular joint (TMJ) in growing rats. METHODS Twenty-four male Wistar rats were weaned at 21 days and divided into control and experimental groups (12 in each group). Control rats were fed a solid diet and experimental rats were fed a liquid diet from 1 to 8 weeks. After injection with 5-bromo-2'-deoxyuridine (BrdU), the animals were perfused and the heads were removed. Serial coronal sections of the TMJ were stained with hematoxylin and eosin, or BrdU immunohistochemistry was done (12 rats in each group). Three dimensions and the thicknesses of the cartilage layers of the TMJ were measured, and cell proliferation in the TMJ was examined. RESULTS After 4 weeks, the height and width of the mandibular fossa and the width and length of the mandibular condyle were smaller in the experimental groups than in the control groups. The cartilage layer in these areas was also thinner at 4 weeks. The BrdU levels in the intermediate zone of the mandibular fossa (at 4 weeks) and the mandibular condyle (at 1 and 4 weeks) were lower in the experimental groups than in the controls. CONCLUSIONS These findings suggest that the growth of the mandibular fossa and mandibular condyle of rats was inhibited by the low proliferative activity of intermediate zone cells induced by liquid feeding.