The tissues covering the bony surfaces and the articular disc of the temporomandibular joint differ from those of most other joints in being not hyaline cartilage but dense fibrous connective tissue. The author investigated elastic system fibers (ESF) in those tissues of the rat. The results were as follows : 1. The temporomandibular joint of the rat showed an appearance of the oxytalan fiber from 17-day-insemination age. 2. The growth of ESF in the temporomandibular joint revealed intensive correlation with increasing functional stress to the joint. 3. ESF in the mandibular condyle had especially a large number of oxytalan type fibers, and many elastase-resistant fibers in it were still noted 150 days after birth. 4. The elastase-resistant fibers were scarcely noted in the articular disc and mandibular fossa since the 25th day after birth. 5. The inferior layer of the articular disc exhibited close network structure of relatively matured elastic fibers. 6. The mandibular fossa and superior layer of the articular disc facing the superior joint cavity had mainly premature ESF and they were few in number. The above results suggested that ESF in the temporomandibular joint appeared in correlation with functional stress imposed on the dense connective tissues and that the greater functional stress at the joint movement was placed on the inferior joint cavity.