Abstract: Based on a large amount of dynamic tri-axial tests, dynamic properties of cement treated soft soils are examined thoroughly. The results show that the dynamic strain d is the most important factor affecting the dynamic modulus and the damping ratio . The dynamic modulus Ed decreases and the damping ratio increases very rapidly with the increase of the dynamic strain d. Both the dynamic modulus Ed and the damping ratio increase with the increase in the cement dosage ratio. The dynamic modulus increases while the damping ratio decreases as the confining pressure 3 increases, at the same strain level. It is further found that the maximum dynamic modulus Edmax increases as an exponential function of the confining pressure 3. The maximum damping ratio max varies from 7% to 30% and decreases as an exponential function of the confining pressure 3. The corresponding formulas are put forward.