A dispersion-strengthened W alloy, W-La2O3, was developed by spark plasma sintering (SPS). The D2 retention and microstructural evolution under 5-keV He irradiation at high temperatures were investigated. Although the density of the W-La2O3 alloy was lower than that of commercially available W, the D2 retention did not change significantly. In addition, the D2 thermal desorption peak, which did not appear in commercial W, appeared at ∼700 K due to the dissociation from D to vacancy clusters. In W-La2O3, the formation of He bubbles was observed at 773 K, 973 K and 1173 K. As the irradiation temperature was increased, void swelling also increased. For the same temperature, the formation of He bubbles was easier for W-La2O3 than for commercial W. This is considered to be the cause of low density of W-La2O3. W-La2O3 had a higher density of vacancies before He irradiation. The suppression of vacancy aggregation induced by the dispersion of La2O3 as the second phase appeared only at a high irradiation doses. •The density of the W-La2O3 was low, however the D2 retention did not change significantly.•In W-La2O3, the formation of He bubbles was observed at 773 K, 973 K and 1173 K.•At the low He irradiation dose, void swelling of W-La2O3 irradiated at 1193 K was higher than that of commercial W.•At the high He irradiation dose, void swelling of W-La2O3 irradiated at 1193 K was lower than that of commercial W.