The phases in the surface layer irradiated by high-energy electron beam were quantitatively analyzed by M ssbauer spectroscopy. A plain carbon steel, a gray cast iron, and a TiB₂/steel surface-alloyed material were irradiated by using an electron accelerator (1.4 MeV), and then their microstructures were examined by using m ssbauer spectroscopy as well as optical microscopy. Upon irradiation, the unirradiated microstructures containing ferrite-pearlite, flake graphites and the pearlite matrix, or TiB₂ powders on the steel surface were changed to martensite-bainite, martensite-ledeburite-austenite, or ferrite-bainite-pearlite, respectively, depending on the material composition and the irradiation condition. These M ssbauer analysis data matched well with the microstructures of the irradiated surface layer. Thus the M ssbauer ,spectroscopy in conjunction with microstructural observations was very useful in quantifying the phases in the complex microstructure formed by electron beam irradiation.