Tungsten (W) based materials for fusion reactor applications have been developed in Japan for the last decade to improve thermo-mechanical properties and tolerance with respect to neutron-irradiation ef- fects. Potassium (K) doping for dispersion strengthening and alloying by rhenium (Re) for solid solute softening and strengthening were applied to W fabricated by powder metallurgy. Thereby modified W materials, e.g. K-doped W and K-doped W-3%Re, demonstrated a higher recrystallization temperature threshold, an increase in strength and ductility, and a reduction in ductile-to-brittle transition temper- ature (DBTT) compared to pure W in the non-irradiated state. Embrittlement caused by displacement damage and its amplification due to solid transmutation products is expected to be an intrinsic issue of W based materials under neutron irradiation environment inherent to future fusion reactors. In this paper, the effect of K-doping and alloying by Re on the neutron-irradiation-induced embrittlement of W was investigated at neutron fluence causing a considerable amount of solid transmutation products.