The properties and electrical conductivity at early age of magnesium phosphate cement (MPC) was studied. Electrical resistivity or conductivity had been used for explaining the microstructure development of cement materials. In the current study, an electrodeless resistivity meter (ERM) was used to study the early property of MPC, which was mixed with and without fly ash respectively. The hardening process was investigated by conductivity variation, incorporating with strength development and temperature rise during the initial reaction of MPC with water. The products and microstructure morphology of MPC paste were analyzed. Results showed the mechanical property of MPC can be improved by fly ash. At the same time, fly ash lowers the maximum temperature rise during initial reaction. The electrical conductivity results divide the hardening process of MPC into three stages: acceleration, deceleration and stabilization. The current study showed conductivity measurement is an excellent method to explain the hardening process of MPC. © (2013) Trans Tech Publications.