The subgingival dental calculi of people in their twenties and that of people over forty were compared to examine changes in structure and composition. The calculus samples of the older group were green, gray, and dark brown in contrast to that of the younger group. On the calculi of the older group, polygonal structures, flake-like structures, and bacillus-like structures were common. In the calculi of the younger group, small spherical structures were commonly observed. EPMA analysis revealed the composition of the calculi of the younger group contained higher levels of Na than that of the older group, while that of the older group contained higher levels of O, Ca, P, and Mg compared to the younger group. The Ca/P molar ratio was 1.75±0.39 on average in the younger group. The Ca/P molar ratio was 1.50±0.21 on average in the older group. HA was detected in the younger group, and W was detected in the older group by X-ray diffraction method. The analysis results of EPMA and the result of the X-ray diffraction method were in harmony. It is possible that the difference in crystal type and composition of subgingival dental calculi between the two groups is due to age.