Using molecular dynamics simulations, the microstructureevolution of nanocrystalline Ta under uniaxial tensile loading isinvestigated. The results show that stress-induced phase transitions fromBCC to FCC and HCP structures may take place during the deformation process. Themaximum of the fraction of FCC atoms varies with the tensile strengthlinearly, by which we can find a critical stress when the phase transitiontakes place. The higher the strain rate is, the later the phase transitionoccurs. Intergranular fracture is also found during the deformationprocess. Crack-formation strain is influenced not by the mean grain size, butalso by the strain rate and the simulation temperature.