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The changes of flow stress in voids-free, and HV and FV films are related to the dislocation density in the strain processes. Following the decrease of relative stacking faults, the decrease of flow stress in FV films is faster than that in HV film. Nanocrystalline ultrathin metallic thin films have various applications for which mechanical properties and durability are important, such as electrodes and electrical interconnects. We investigated the effect of voids on mechanical behavior of thin nanocrystalline gold films using molecular dynamics. Different kinds of voids were considered. We found that the nature and geometry of the void was important for the mechanical properties in this model ductile material. It was found that in the half voids films the flow stress decreased following the decrease of mass density with a linear relation. For the full voids films, the strain–stress curve was different from that of voids-free film and half voids films. The plastic deformation could be activated with smaller amount of dislocations. Following the strain increase over the strain of ultimate tensile strength, the flow stress decreased. This implied that the voids which penetrated through the films would weaken the ductility of films. The deformation main mechanism was grain boundaries sliding with voids coalescence. On the contrary, if the void depth was less than the thickness of film, the ductility of film wasn't influenced apparently, though the ultimate tensile strength decreased with the increase of voids size and decrease of mass density. [ABSTRACT FROM AUTHOR]