This paper describes an anisotropic elastoplastic based constitutive model for describing the behaviour of lignosulfonate stabilized soils. The proposed model is an extension of the earlier model developed by Dafalias (1987). The theoretical formulations of the current model were based on the frame work of critical state concept. The novel feature of this model is the incorporation of a material constant b, which takes into account of the degree of cementation. It is demonstrated that the model can capture the behaviour of lignosulfonate treated soil.