Abstract: The expansive unsaturated soils are characterised by the behaviour of volume increase and strength reduction during wetting, which may cause nonuniform foundation settlement and further result in cracking of overlaying buildings. A factor accounting for the plastic volumetric expansion is developed, which is associated with the dry density and overconsolidation ratio. This factor is subsequently introduced to the framework of the existing unified hardening (UH) model for the overconsolidated unsaturated soils to properly describe the characteristics of volume expansion and strength reduction during wetting. Compared with other existing models, the model requires fewer parameters, and can adequately account for the influences of the overconsolidation ratio and initial dry density on the stress-strain relationship of the expansive unsaturated soils. Meanwhile, the proposed model can describe the strain-softening behaviour of the expansive soils in the overconsolidated state. This model can be reduced to the existing UH model for the overconsolidated unsaturated soils when the factor accounting for the plastic volumetric expansion becomes zero. The capability of the proposed model in quantitatively describing the stress-strain characteristics of the expansive overconsolidated unsaturated soils is verified by comparing with the existing experimental results.