Salivary calculus is an ectopic calcification of high frequency in oral region. Many previous reports on the composition and structure of salivary calculus only showed apatite crystal as the main constitution but were not sufficient to clarify the formation mechanism. In this study, structural properties of the salivary calculus were investigated by the high-reproducibility non-destructive method such as optical microscope, micro-CT, micro-FT-IR and micro-XRD. In some cases, SEM, BSI, and EDS analysis were also carried out. The results showed that the salivary calculi were grouped into three by structure, and grouped into three or four by chemical composition and crystal components. The difference in structure and composition should be reflected by the formation mechanism.