PURPOSE: To provide a racket gut consisting of an Ni-Ti shape-memory alloy forming a martensite phase metal texture at normal temperature, having high breaking strength and small diameter and resistant to deterioration of quality.

CONSTITUTION: The objective gut forming 100% martensite phase at normal temperature and transforming to austenite phase at ≥50°C is produced by casting an Ni-Ti alloy having an atomic ratio of e.g., 50:50, forming the ingot into a thick rod by hot-rolling, repeating the cold working and annealing to obtain a thin wire of 0.2-0.8mm diameter, maintaining the wire at 400-500°C for several min to 1hr (shape-memory heat-treatment) and cooling to normal temperature.