Abstract: A numerical method for the prediction of effective elastic modulus of concrete with interfacial transition zone (ITZ) is proposed. The Generalized Self Consistent Method (GSCM) was adopted to calculate the effective properties of the equivalent two-phase sphere model, which is composed of aggregate and ITZ around it. The Representative Volume Element (RVE) was generated by random aggregate model with equivalent particles to predict the elastic modulus of concrete. By applying the homogeneous displacement boundary condition on the RVE, the stress and strain fields can be calculated using the numerical method. The effective elastic moduli were predicted by the micromechanical numerical homogenization method. The results show that the predicted effective elastic moduli of concrete with different volume fraction of aggregate agree well with those from the tests. The thickness of interfacial transition zone has a great influence on the effective modulus of concrete.