Interfacial transition zone (ITZ) between cement matrix and aggregate is regarded as a weak phase that affects the mechanical properties and durability performance of concrete. Therefore, resolving ITZ around aggregate has always attracted great attentions in concrete research. Due to the limitation of resolution, using industrial X-ray computed tomography (XCT) to address three-dimensional (3D) morphology of ITZ becomes a challenge. However, the extremely high X-ray attenuation of mercury can greatly increase the contrast of XCT images when the pores of ITZ are filled with mercury. This regime allows visual characterization of ITZ for cement-based materials after mercury intrusion porosimetery (MIP). A glass rod was used as an aggregate to fabricate connected matrix-aggregate ITZs. The results show that the residual mercury droplets in pores after MIP enhance the gray values of ITZ, thus addressing the 3D structure of ITZ. The findings provide a new path to exploring the pore structure of matrix-aggregate ITZ in cement-based materials.