Crystallographic analysis of plate martensite in an Fe-28.5 at.% Ni alloy was studied by electron backscattering diffraction (EBSD) in a scanning electron microscope equipped with a field emission gun (FE-SEM). It was shown that sound orientation mapping was possible even for the martensite having a high density of lattice defects and the FE-SEM/EBSD could be a strong tool for crystallographic/microstructural analysis of martensite in steels. It was confirmed that the martensite in this alloy held the Nishiyama-Wassermann (N-W) orientation relationship. Variant analysis of every martensite crystal was successfully done from orientation mapping data. It was clarified that a certain rule of variant selection operated within local areas. The procedures of crystallographic analysis of N-W martensite were explained in detail. © 2005 Elsevier Inc. All rights reserved.