A thixotropy model is developed for the prediction of the viscosity of silica suspensions. The model can be applied for the prediction of non-Newtonian viscosity of agglomerative suspensions with particle size distribution. Since the model assumed that the particle shape was spherical, a mixture of mono-modal spherical silica particles was used to prepare the concentrated suspensions. Viscosity measurement results have proved that the present model was able to predict the non-Newtonian suspension viscosity under steady simple shear flow conditions, although more discussion on the physical meaning of inter-particle bonding energy was needed. The applicability of the present model must be checked for the suspensions prepared using non-spherical particles with particle size distribution in the future.