Using molecular dynamics simulations, the tensile deformation behavior for two types of sub-10 nm multilayer nanowires (NWs) have been investigated.For the structure with interfaces perpendicular to the wire axis, the deformation mechanism is changed from interface crossing by dislocations to interface rotation as the layer thickness is decreasing, causing a significantly reduction in yield strength.However, the deformation mechanisms are all accommodated through interface crossing by dislocations regardless of layer thickness for the structure with interfaces parallel to the wire axis.Moreover, the yield strengths in the second structure are found to be controlled by two competing mechanisms: the interface strengthening by increased repulsive force and interface softening by increased dislocation source sites.The sudden stress drop after yielding point in NWs could be explained by the dislocation source-limited hardening mechanism: the more atomic fraction of newly formed stacking faults (SF) after stress drop, the larger normalized stress drop and the larger uniform tensile elongation.For the second structure, the larger total tensile elongation for larger layer thickness could be related to the twinning induced plasticity at the necking position.These findings should have implications for designing functionalized structures and devices in nanoelectromechanical systems.