In order to examine the dynamic characteristics of expansive soil in natural environment, the maximum shear modulus of undisturbed and remoulded Nanyang expansive soil specimens were tested by using a triaxial apparatus equipping with a pair of bender element. The saturated undisturbed Nanyang expansive soil specimen was tested using the bender element to measure the maximum shear modulus under different confining pressures. The maximum shear modulus of the undisturbed and remoulded specimens with the same dry density were measured in wetting-drying processes and analyzed in combination with the void ratio. The test results indicate that the maximum shear modulus of the saturated Nanyang expansive soil increases with the increasing confining pressure. In the relationship between the maximum shear modulus and water content, the drying curve is higher than the wetting one. It is also found that there is hysteretic characteristics in the maximum shear modulus and water content relationship, which is mainly due to the suction effect. Under similar dry density the maximum shear modulus of undisturbed specimen is smaller than the remoulded one. The reason is that there are more large pores in the undisturbed soil. Finally, an existing formula for the saturated soils is improved for predicting the maximum shear modulus of the unsaturated and undisturbed Nanyang expansive soil.