<p>Effects of Al on room temperature super-elasticity of NiTi alloys were investigated. It is found that (1) replacing Ni by Al quickly increased the volume fraction of (Ti, Al)₂Ni phase, significantly embrittled the material and reduced its workability; (2) regardless of which element it replaced, Al significantly destabilized B19′ martensite but promoted R-phase transformation; (3) increasing Al increased critical stresses for R-phase and B19′ martensite phase transformations, Al also encouraged the deformation twinning or dislocation slip, which impeded the stress-induced phase transformation and reduced the super-elasticity of materials at room temperature; and (4) the effect of residual cold work competed with that of Al. At a&#xa0;lower Al level, where deformation twinning or dislocation slip was less active, the effect of residual cold work surpassed that of Al and improved super-elastic behavior after heat treatment at low temperatures.</p>