The measuring tests on the maximum opening distance and the maximum capacity opening distance were conducted on the one hundred normal dental college students and staffs o Seoul National University in order to study the relationships between the maximum opening distance and maximum capacity opening distance. The results were as follows: 1. The maximum opening distance and maximum capacity opening distance were not coincided. 2. The distance of the maximum opening was higher than that of the maximum capacity opening. 3. Physiologic reflex was caused by the water injected into the mouth. 4. The correlation between the maximum opening distance, and maximum capacity opening distance was hardly recognized. 5. Each correlation of the weight height and cheek thickness to maximum opening distance and maximum capacity opening distance was not recognized.