Molecular dynamics (MD) methods are utilized to study the displacement cascades in α-Fe containing different concentrations of substitutional He atoms. Primary knock-on atom (PKA) energies, Ep, from o.5 keV to 20 keV are considered at a temperature of 100 K and 600 K, and the results are compared with those performed in pure α-Fe. There are distinct differences in the number and size of defect clusters within displacement cascades with and without substitutional helium atoms. Particularly, the number and size of helium-vacancy clusters generally increase with increasing helium concentration and PKA energy. However, the number of He-vacancy (He-V) clusters increases with increasing temperature, the mean size of He-V clusters is independent on temperature for the same He concentration and energy recoils.