The role of the grain boundary on the room temperature resistivity of Pb(Fe 1=2 Nb 1=2 )O 3 (PFN) was investigated using parameters such as temperature dependence of resistivity, complex impedance spectroscopy and X-ray photoelectron spectroscopy. The low resistivity of PFN has been reported to be due to the electron hopping between Fe 2þ and Fe 3þ driven by the reduction of PFN. However a reconsideration of the reduction equilibrium constant (K Re ) revealed that this theory could not fully explain the effect of the sintering temperature on the room temperature resistivity. The role of the grain boundary on the total resistivity was introduced in order to account for this behavior, which was confirmed by complex impedence spectroscopy. Furthermore, the annealing data and X-ray photoelectron spectroscopy (XPS) results showed that the grain boundary properties were irreversibly changed at 1423 K, which appeared to be due to Pb volatilization.