Cement-based material is a typical porous composite material. Pore structures and interfacial properties of cement-based materials are influenced properties of ion transport behavior and durability. This study determines pore structure by employing mercury intrusion porosimetry (MIP), with mortar specimens manufactured with three different water-cement (w/c) ratios and five volume proportions of fine aggregate to investigate interfacial properties. The experimental results show that total mercury intrusion decreases with an increase in sand volume proportion when comparing the same w/c ratio. The calculated mercury intrusion of interfacial transition zone increases with w/c and the volume proportion of fine aggregate.