Effect of 25keV He ion irradiation on three model Fe 100− x Cr x alloys (x=5.8, 10.75 and 15.15) was investigated by means of the conversion electron Mössbauer spectroscopy. A short-range ordering (SRO) parameter concerning a distribution of Cr atoms within the first-two neighbour shells, <α 12 >, for all three non-irradiated samples was positive, hence indicative of ordering, yet its amplitude, hence the degree of ordering, was decreasing with x. For the samples irradiated to the dose of 1.2·10 17 He + /cm 2 (7.5dpa) <α 12 >was unaffected for x=5.8 and 10.75 but its value was negative for x=15.15 i.e. an irradiation-induced inversion of the SRO-parameter occurred.