Studies have been made on the void swelling of solution-annealed Fe-15Cr-20Ni alloy irradiated with 180 keV protons at temperatures from 723K to 923K. The displacement damage levels were 5, 10 and 20dpa for samples preinjected with 10 appm He at room temperature, and 5dpa for samples without He. In comparison with previously reported results of nickel-ion bombardment, void nucleation seemed to finish at earlier stage of irradiation in samples injected with He. Subsequent void growth was rather fast and, as a consequence, relatively large swelling was observed. Void microstructure and swelling were similar at 723 and 773K between the samples with and without preinjected He, but they were quite different at 823K probably due to helium effect which persists even at high temperatures. The results suggest that hydrogen introduced into the material by proton irradiation may play a significant role, which is similar and comparable to that of helium, in the microstructure evolution during irradiation at temperatures up to 773K.