Nanocrystalline (NC) Ti494Ni50:6 alloy with a different mean grain size in a range of 20-100 nm has been successfully produced using severe plastic deformation by high pressure torsion and further annealing at various temperatures. The features of microstructure and martensitic transformation of the NC TiNi have been studied. During tensile tests the effects of the grain size on mechanical properties at room and elevated temperatures are studied and discussed. The NC TiNi exhibits an unusual increased strength but low ductility at room temperature. However, it demonstrates enhanced strength and ductility at higher temperatures.