The phase transformation and superelastic behavior of nanocrystalline Ni48Ti50Mo2 alloy wires were investigated. Nanocrystalline (NC) alloys were obtained via severe plastic deformation of cold-drawing followed by annealing at low temperatures. The results indicate that the NC Ni48Ti50Mo2 undergoes a single-step B2→R phase transformation and a two-step B2→R→B19′ phase transformation in coarse crystals (CG). The NC alloy wire exhibits 8 % recoverable strain under a tensile stress of 1.1 Ga and superelasticity exists in a wide temperature range from −60 °C to 100 °C. After 50 cycles of tension fatigue testing, the superelastic upper plateau stress reduction rate is 7 % with almost no residual strain accumulation, which has excellent superelastic stability compared with fine crystals and coarse crystals. Transmission electron microscope (TEM) reveals an average grain size of 20 nm. The stable superelasticity is attributed to the nanocrystalline reinforced matrix, which hinders dislocation generation and slip.