Various heat treatment conditions with temperature scans of 300-700 °C, and annealing time scans of 1-4 hours were adopted in the annealing of Ti-49.5at.%-Ni shape memory alloy ultra thin wires. The mechanical hysteretic curves and the crystal morphology were obtained by the tensile-recovery testing and scan electric microscopes (SEM). The result shows that the shape memory effect of Ni-Ti alloy first decline after rising with the heat treatment temperature increases. Alloy with heat treatment effect in 500°C, presents the best. Time is not a significant factor for heat treatment.