This study investigates the effects of aging on the shape memory and superelasticity behavior of a Ni-rich Ni54Ti46 (at%) alloy. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM) and compression test (thermal cycling under stress and superelasticity) were carried out after 3 h agin;g from 450 degrees C to 600 degrees C. The alloys show recoverable shape memory effect with transformation strains of about 1% and narrow hysteresis under high stress levels. The work output of 14.1 Jg(-1) was observed at an ultra-high stress level of 1500 MPa after 600 degrees C 3 h aging. 450 degrees C 3 h aging resulted in a very narrow temperature hysteresis of 8 degrees C under an ultra-high stress level of 1500 MPa. At room temperature, the superelastic response with 4% total strain was obtained even when high stress level of 2000 MPa is applied after 550 degrees C 3 h aging.