School children with the average size of the head were studied as the experimental subjects. (1) The left-right diameter and area of the maxillary sinus of 5th year. boys and 2nd year girls were remarkably increased. The up-down diameter of 5th and 6th year boys and the 2nd and 5th year girls and the anterior-posterior diameter of 3rd and 6th year boys and of 2nd and 5th year girls were also remarkably increased. (2) The sinus bottom of first year boys was located at 2/3 of the lower nasal canal and that of first year girls at 5/9 of the lower nasal canal. The sinus bottom of 4th year boys and 2nd year girls was of the same height as the nasal bottom. (3) Before the cuspid grew, the external edge of the cuspid sack was 1.0cm outside of the extremely external edge of the lower nasal canal, its upper edge 1.0cm. above the nasal bottom and its posterior edge within 2.0cm straightly backward from the tip of the spina nasalis anterior. (4) The distance from the dental sack (at the root of teeth) to the sinus bottom was short in first, 2nd, 3rd and 4th year pupils (cuspid, 2nd bicuspid 2nd and 3rd molar teeth), in 5th pupils (2nd bicuspid, 2nd and 3rd molar teeth) and in 6th pupils (first, 2nd and 3rd molar teeth).