The purpose of this study was to investigate the distribution of CGRP immunoreactive nerve fibers in rat squamosomandibular joint with postnatal development. Squamosomandibular joint with adjacent tissue of 8 groups of rats(1, 5, 10, 15, 20, 25, 35-postnatal day and adult groups) were removed on bloc and processed for immunohistochemistry and were subjected to light microscopic examination. The results obtained were as follows; 1. The anterior portion of the articular disk was most densely innervated, followed by the posterior, lateral, and medial portions in each group. 2. Increase of CGRP immunoreactive nerve fibers was evident in 10, 15, 20 postnatal day groups. 3. Almost no CGRP immunoreactive nerve fibers were observed in articular surface of disk proper, mandibular fossa and condyle head of each group. These result suggest that CGRP immunoreactive nerve fibers increased in synovial membrane and peripheral portion of articular disk during 10-20 postnatal day may play a important role in squamosomandibular joint function after weaning period.