The dynamic shear modulus of human dentin was measured using a torsion pendulum between 23°C and 150°C. Dentin had a relatively stable modulus in spite of increasing temperature. The shear moduli at 37°C for 20 specimens were in the range of 5.77×1010 dyne/cm2-1.06×1011 dyne/cm2. These values differed little from that for composite resins (6.77×1010 dyne/cm2). The peak in the distribution curve of the mechanical loss tangent was observed at nearly 75°C. The values for the loss tangent were markedly low in comparison with that for composite resins. Though the number of samples was small, it seemed that there was no significant correlation between the shear modulus and the patient's sex, age and tooth type.