During fusion reactor operation, transmutation elements such as rhenium (Re) and osmium (Os) are produced from tungsten (W) upon neutron irradiation. Thus, the pure W becomes W-Re or W-Re-Os alloys and its physical properties gradually change. The irradiation hardening, microstructural changes, and physical properties of these transmutation elements of W are here investigated. Tungsten-based model alloys are fabricated and neutron irradiation is performed in the JOYO fast test reactor. The irradiation dose and temperature are 0.17-1.54 dpa and 400-750 °C, respectively. Vickers hardness measurements, microstructural observations, and electrical resistivity measurements are subsequently performed. The effects of the microstructural evolution on the irradiation hardening and electrical resistivity are discussed.