The impact of heavy metal oxides, such as ZnO, PbO and CuO, on the setting time and mechanical properties of cement pastes was investigated. SEM and XRD were used to examine the microstructure of cement paste as well. The results show that the setting process is greatly influenced due to the addition of heavy metal oxides, even with low contents. By the contrast, however, the mechanical properties are less influenced. The change of the microstructure of cement pastes with heavy metal oxides depends on the type of heavy metal. It is revealed that the XRD peaks of CH and AFt deviate slightly from the common positions.