Abstract The process of sulfate attack on cement mortar was studied from influences of interfacial zone between aggregate and bulk paste. The influences are the content of interfacial zone and the structure of interfacial zone. The mortar samples were prepared in accordance to a series of volume fraction of aggregate. To improve the structure of interfacial zone, a pretreated quartz aggregate was used, which is composed of hydraulic surface layer and inert core. The results showed that the interfacial zone was an important influencing factor. The mortar resistance to sulfate attack was reduced with the increase in content of interfacial zone but was enhanced by the improvement of the structure of interfacial zone.