In this paper, the elastic modulus measuring of human cementum is studied. The average value of the elastic modulus measured from 100 specimens is E=2.398±0.455 GPa. The specimens were made from incisors, canines, bicuspids, and molars. The testing was done on type AG-10TA electronic-mechanical universal material testing machine. It was verified by mathematical sttistics that the probability distribution of measured data obeys normal distribution. By the great difference in elastic moduli between cementum and dentin it is explained that 1. why more cementum grows at the root apexes; 2. the behavior of cementum must be taken into consideration when the stress analysis for teeth is carried out.