The compositional profile, distribution of the phases and the ordering behavior in the interdiffusion layer of the PNN/PZT functionally gradient piezoelectric ceramics have been investigated by electron probe microbeam analyses (EPMA) and transmission electron microscopy (TEM) respectively. The results show that the thickness of the interdiffusion layers (d) for Ni2+, Nb5+, Ti4+ and Zr4+ ions are ordered as d(Ni)(2+) > d(Nb)(5+) > d(Ti)(4+) > d(Zr)(4+). It is demonstrated by TEM observation and selected area electron diffraction (SAED) patterns that a clear interface between the rhombohedral and pseudocubic phases exists in the interdiffusion layer. The SAED studies also reveal the presence of F spots along the [111] direction of the perovskite cubic unit cell. The origin of this superstructure is determined.