The human teeth have the attrition by the physiological function after the teeth eruption, and the teeth change continuously, as we grow older. So, our teeth are the hard tissue organ and remain their form, even after our death. These facts are very important in anthropology and forensic odontology. But if we don't use the scientific standard about the condition of the attrition, it is not easy for us to guess our age from the degree of the teeth attrition. So, I examined the attritted condition of 3729 exodontic teeth, about whose background I knew very well and investigated every changing condition of them, as years went on. From them, I got the following results. 1. As for the form of attrition, the range of attrition has been expanded, as we grow older, but our teeth except the first molar have little attrition under 20 years old. After 20 years old, our teeth change from the incipient into the matured type gradually. As the eruption of the first molar is earlier than the others, I recognize the attrition even before 20 years old. 2. As we grow older, the degree of attrition gets high, the strength of it differs among different kind of teeth, and even if the teeth are the same kind, the strength is different from the position. The lower first molar shows the highest degree of attrition early and the front teeth show the lowest degree of attrition. This shows the difference from the strength in biting force. In the upper front teeth, the marginal ridge of lingual surface show the highest degree of attrition : in the upper molars, the lingual cusp show the highest degree of attrition : in the lower molars, the buccal cusp show the highest degree of attrition. 3. As for the degree of abrasion in the incisive edge of the front teeth, upper canine shows the highest degree and lower incisor shows the second highest degree. It progresses gradually, as years go on. 4. As for the difference from the strength in teeth attrition between mesial surface and distal surface, I have found lots of mesial attrition types generally, but I have found lots of distal attrition types in the premolars of upper and lower part, and lower canine. 5. As for the relation between the measurement of crown length and the degree of attrition, I have found a little difference from the different kinds of teeth, but when the degree of attrition gets one degree high generally, the crown length reduces 0.5-1.0mm. 6. The degree of the teeth attrition depend on food, the condition of biting, the strength of biting force, the age of teeth eruption and the individual habit of attrition. As the environments have a great influence with the attrition, when we are going to guess the age from the attrition. We should consider such factors as I mentioned and decide the correct age.