This paper presents an experimental and numerical investigation of the undrained shear characteristics of an undisturbed clay with higher plasticity index (PI=69), using the simple procedure for the undrained shear behaviour of Ko-consolidated cohesive soils estimated by plasticity index. Comparisons were made between the experimental data and the model simulations concerning the undrained triaxial compression and extension loadings, for the purpose of checking the applicability of the analytical results obtained from the adopted model and soil parameters. Reasonable agreement has been obtained between the observed and the computed results of the undrained shear behaviour of the undisturbed clay with higher plasticity index. It is concluded that the applicability of the author's method for the undrained shear behaviour of the undisturbed clay with higher plasticity index is reconfirmed.