The interfacial transition zone (ITZ) around aggregates is widely accepted as the weakest link in concrete that changes its elastic behaviour from brittle elastic to quasi-ductile on the application of external loads. In this paper, the influence of ITZ on the elastic properties of concrete is modelled using a multiscale micromechanics approach that includes the effects from the scale of the cement particles to the scale of aggregates. The approach considers the complexities present at different scales of concrete, such as aggregates of different types and size, microstructural features of the interfacial transition zone (ITZ) and bulk cement paste (BCP). The microstructure of ITZ and BCP is simulated using a vector based microstructural modelling platform (µic). The capability of the model to predict the elastic modulus of concrete is shown by comparing the model predictions with experimental results from the literature. Parametric studies on microstructural features of ITZ show that the preferential deposition of portlandite (CH) has a significant influence on the early age elastic modulus. Comparison of the predictions from the developed approach with predictions from the Mori-Tanaka method shows that the ITZ has the potential to reduce the macroscopic elastic modulus, however, the reduction in the elastic modulus in the ITZ is compensated by the increase in the elastic modulus of the BCP. © 2020 Elsevier Ltd