This study was designed to investigate the growth amount and rate of mandible by the measurements of mandibular lateral surface and the relationship of peak growth increments between mandible and body height. The sample consisted of twenty-five boys and fifteen girls between the ages of 6 and 13 The surface of mandible was measured from digitized roentgenocephalometric analysis (A 27 point mandibular model) The findings of this study can be summarized as follows 1. No significant difference was found between mandibular lateral surfaces of the both sexes at the ages studied. 2. The mean growth amount of mandibular lateral surface from 6 to 13 years of ages was 9.09cm^² in boys and 8.29cm^² in girls, and the mean growth rate was 46.07% in boys and 42.57% in girls 3. The prepubertal peak growth increment in mandible was found between the ages of 11-12 in girls and 12-13 in boys 4. The prepubertal peak growth increments of mandible occured one year later that of body height in boys and girls.