Interfacial microstructure characteristics of four different aggregatecement paste were investigated by scanning electron microscope(SEM) and energy dispersive spectrometer(EDS). The four aggregate were sourced from sandstone, marble, syenite and basalt, respectively. The ultimate tensile properties of concrete with those four different aggregates were discussed. Test results show that the water absorption at saturated surfacedry basis varies among the four aggregates and affects the chemical composition of hydration products in interfacial transition zone of aggregatecement paste, and then affects the interfacial microstructure characteristics. Calcium hydroxide crystal is identified more clearly to be concentrated along the aggregatecement paste interfacial transition zone of sandstone and marble than those of syenite and basalt. The width of interfacial transition zone varies among four aggregates, i.e. in descending order：marble, sandstone, syenite and basalt. It is also implicated that the interfacial microstructure characteristics play a role in affecting the axial tensile stressstrain behaviors of concretes.