We deal with scaling relations based on fractal theory and rheological properties of a colloidal suspensionto determine a structure parameter of colloidal aggregates and thereby predict shear viscosity of the colloidal suspension using an effective-medium model. The parameter denoted by β is m(3-df), where m indicates shear rate (D) dependence of aggregate size R, i.e. R∝D.m, and df is the fractal dimension for the aggregate. A scaling relation between yield stress and particle volume fraction φ is applied to a set of experimental data for colloidal suspensions consisting of 0.13 μm zinc oxide and hydroxyethyl acrylate at φ = 0.01-0.055 to determine β. Another scaling relation between intrinsic viscosity and shear rate is used at lower φ than the relation for the yield stress. It is found that the estimations of β from the two relations are in a good agreement. The parameter β is utilized in establishing rheological models to predict shear viscosity of aggregated suspension as a function of φ and D. An effective-medium (EM) model is employed to take hydrodynamic interaction between aggregates into account. Particle concentration dependence of the suspension viscosity which is given in terms of volume fraction of aggregates φa instead of φ is incorporated to the EM model. It is found that the EM model combined with Quemada’s equation is quite successful in predicting shear viscosity of aggregated suspension.