At room temperature, oxide dispersion strengthened (ODS)-Fe (Fe-2% Al2O3) and pure Fe were implanted with 140-keV helium ions by doses up to 1e+15, 5e+15, and 1e+16/cm(2). Vacancy-type defects induced by the implantation were investigated with positron-annihilation spectroscopy (PAS). Defect profiles of the S-parameter derived from PAS as a function of positron incident energy up to 20 KeV were analyzed. The S-parameter of the damaged layers in the ODS-Fe tend to be smaller than those in the pure Fe when the irradiation doses reach 1e+16/cm(2). This finding indicates that the ODS-Fe sample exhibits a higher irradiation resistance than the pure Fe. The reason might be that helium irradiation-induced point defects in ODS-Fe are trapped and annihilated at interfaces between the Fe matrix and the Al2O3 nanoparticles. Vacancy clusters and helium-vacancy complexes were identified as the main defects. Through the S-W curves, however, we observed only one type of defect in the irradiated ODS-Fe. While for the pure Fe case, things seem to be more complicated, where the surface and the bulk have different types of defects.