In Newtonian mechanics, shear resistance of material is assumed to be linear proportion to shear rate, in which the proportional constant is defined as a coefficient of viscosity. However, the rate-dependent or viscous behaviour of soil can not simply assume to be linear, but it can be explained using Rate Process Theory (Mitchell and Soga, 2005). The rate effect on shear strength of soil and creep settlement are two well-known examples of the viscous behaviour of soil. In addition, Vaid and Campanella (1977) have shown an experimental evidence of the rate effect on the shear strength of Haney Clay. This paper aims to present the non-linear viscous behaviour of Bangkok Clay using an experiment programme and modelling. The experiments are performed on normally consolidated clay which taken from the Centre of Bangkok. All specimens are isotropically consolidated and undrained compression sheared varying with five different shear rates. The rate-dependent hyperplasticity model (Puzrin and Houlsby, 2003 and Likitlersuang and Houlsby, 2006) based on Rate Process Theory are employed in this study. The model is calibrated against the undrained triaxial sheared tests of Bangkok Clay.