In this paper, a two-step model is proposed to predict the effective chloride diffusivity of cement paste and cement mortar. The prediction effective chloride diffusivity results of cement paste and cement mortar are compared with two different experimental method results. In the two-step model, the effective chloride diffusivity of cement paste is predicted based on the porosity and the effective diffusivity of the solid phase using the general effective media (GEM) model. Based on the GEM model, the effective chloride diffusivity of cement mortar is predicted by the composite spheres assemblage (CSA) model, which considers the aggregate volume fraction and the effective diffusivity of the interfacial transition zone (ITZ). As important inputs of the model, the porosities of cement paste and mortar are obtained by low field nuclear magnetic resonance (LF-NMR). The effective chloride diffusivities of cement paste and mortar are also determined by a newly proposed modified noncontact electrical resistivity measurement (MN-CM) based on the Nernst-Einstein equation and the rapid chloride migration test (RCMT). The results show that the effective chloride diffusivities from the proposed prediction model is in good agreement with the experimental results. The proposed prediction model could be used to predict the diffusivity of cement-based materials.