TiNi alloys, with their unique shape memory effects and super elastic properties, occupy an indispensable place in the family of metallic biomaterials. In the past years, surface treatment is the main technique to improve the bioinert nature of microcrystalline TiNi alloys and inhibit on the release of toxic nickel ions to obtain excellent osteogenesis and osseointegration function. In the present study, nanocrystalline Ti_49.2Ni_50.8 alloy has been fabricated via equal channel angular pressing (ECAP), and the in vitro and in vivo studies revealed that it had enhanced cell viability, adhesion, proliferation, ALP (Alkaline phosphatase) activity and mineralization, and increased periphery thickness of new bone, in comparison to the commercial coarse-grained counterpart. These findings indicate that the reduction of grain size is beneficial to increasing the biocompatibility of Ti_49.2Ni_50.8 shape memory alloy.