One of the most important problems in the field of nuclear industry is the relationship between irradiation-induced damage and the resulting induced mechanical response of the target metal and in particular ferritic base steels. In this work molecular dynamics simulation is used to simulate the nanoscale interaction between a moving dislocation and a defect, such as a cavity, as void or He bubble. The stress–strain curves are obtained under imposed strain rate condition using the atomic potentials based on the Fe potential of Ackland et al. 1997 for a void and He bubble as a function of He content and temperature. It appears that a 2 nm void is a stronger obstacle than a He bubble at low He contents, whereas at high He contents, the He bubble becomes a stronger obstacle. With increasing temperature the escape stress decreases and at the same time there is increasing degeneracy in the type of interaction.