Teratoma is very rarely developed in the third ventricle. We report a case of third ventricular mature teraroma in 12 year old boy with headache and precocious puberty. In TlWl and Gd-DTPA enhanced TlWl, the mass in the third ventricle showed mixed signal intensities with signal void and partial contrast enhancement. The tumor was confirmed as a mature teratoma including teeth and fatty tissue.