TiNi shape memory alloy has been widely used in diverse areas of applications because of its superior shape memory and superelastic properties. Another important aspect of this material is that it is susceptible for solid-state amorphization. In fact the first report of electron-beam induced amorphization was on TiNi. More recently, nanocrystallization/amorphization by various methods of severe plastic deformation (SPD) was reported; the mode of deformation includes mechanical milling, cold rolling, high pressure torsion as well as shot peening. In the present study, the effect of nanocrystallization/amorphization by SPD (cold rolling and high pressure tortion) on mechanical property was investigated on TiNi shape memory alloys. Samples of TiNi alloy with various compositions were homogenized at 1173 K for 3.6 ks and water quenched. They were then cold rolled at room temperature. The maximum thickness reduction was 50 %. Rolled samples were then heat-treated at various temperatures from 473 K to 573 K. Martensitic transformation (MT) temperatures were measured on DSC. Microstructural observations were made on TEM. Mechanical properties of the rolled and heat-treated samples were investigated by tensile tests. After 40~50 % cold rolling the sample became a mixture of amorphous and nanocrystalline regions. Grain boundaries surrounding the nanocrystals appeared rather fuzzy. After the heat treatment at 573 K for 3.6 ks amorphous region remained but the nanocrystalline boundaries became sharp and well-defined ones. DSC measurements revealed that cold rolling over 30 % reduction suppresses the MT. After the heat treatment for 3.6 ks at 573 K, no trace of MT was found. After 3.6 ks at 673 K, clear R phase transformation peak and very broad MT peak appeared on cooling. As the heat treatment temperature increase the MT temperature peak became more pronounced and shift towards the MT temperature in the samples before rolling. The 50 % rolled samples exhibited typical superelastic behavior after treated at 673 K for 1.8 ks, while the samples after treated lower temperature exhibited about 3% superelastic strain without clear stress plateau. The hysteresis in the stress-strain curve was much smaller when tested without heat treatment. Similar tendency has been observed for HPT samples. Correlation between the mechanical properties and the microstructure in SPD TiNi will be discussed.