Abstract: Recycled aggregate concrete is regarded as a kind of heterogeneous composite material composed of mortar matrix phase, recycled aggregate phase and the interfacial transition zone (ITZ-2) phase between new and old mortars. Among them, mortar matrix phase is composed of fine aggregate, hardened cement pastes and the interfacial transition zone (ITZ-1) between them, while the recycled aggregate phase is composed of old aggregate, attached old mortar, old interfacial transition zone (ITZ-3) between them. Based on the N-layer spherical inclusion theory with considering the influence of microscale phase, a five-phase multiscale model of effective chloride diffusion coefficient of recycled aggregate concrete was established. The accuracy and validity of the proposed model were verified by comparing between the experimental and predicted results of steady-state chloride diffusion coefficient of hardened cement paste, mortar and recycled aggregate concrete, respectively. Finally, the influence of the key parameters including the chloride ingress time, the volume fraction of recycled coarse aggregate and the attached mortar content on effective chloride diffusion coefficient was further discussed. The results show that the predicted effective diffusion coefficient agrees well with the experimental results obtained in the literature. It indicates that the proposed model can be universally used to predict the effective chloride diffusion coefficient of recycled aggregate concrete, which provides a theoretical basis for durability evaluation and service life prediction of recycled aggregate concrete exposed to chloride salt environment.