Using molecular dynamics simulations, the influence of transverse tensile stresses on theplastic deformation behaviour of nanocrystalline (NC) Ni under tension has been investigated. Thesample with an average grain size of 20 nm was created using a Voronoi construction, and twodifferent tensile tests of the sample were performed at a constant strain rate. The simulation resultsrevealed that more partials were emitted from the grain boundaries and propagate into the graininteriors after adding the transverse tensile stress, enhancing the dislocation density in the graininteriors. This increased dislocation density can cause additional strain hardening observed in thestress strain curve. Meanwhile, it was observed from microstructures that nanovoids are easier toform and coalesce into cracks under the biaxial stress state, causing strain softening. The twocompeting effects of the transverse tensile stress on the plastic deformation behaviour of NC Niresulted in the flow stresses from 4% to 10% strain in the biaxial stress state slightly larger thanthose in the uniaxial stress state.