The interactions between dislocations and twinboundaries (TBs) are significantly affected by both intrinsic material properties and extrinsic factors, including stacking fault energy, the energy barriers for dislocation reactions at TBs, twin thickness and applied stress. In this study, dislocation–TB interactions in grains with different dislocationdensities were investigated and we conclude that the dislocationdensity also affects the dislocation–TB interactions. In a twinned grain with a low dislocationdensity, a dislocation may react with a TB to fully or partially penetrate the TB or to be absorbed by the TB via different dislocation reactions. Alternatively, in a twinned grain with a high dislocationdensity, dislocations tangle with each other and are pinned at the TBs, thereby making it unfavourable for further dislocation reactions to mediate dislocation penetration across the TB. This leads to an accumulation of dislocations at the TBs, raising the local strain energy, which, in turn, is released by the activation of secondary twins by partial dislocation emissions from the other side of the TB