The Nb content of TNTZ (Ti-29Nb-13TaA6Zr) was changed by 1 mass% to 2 mass% below 30 mass%. The change in the behavior of functionalities such as superelasticity and the shape- memory effect was investigated by tensile loading-unloading tests, X-ray analysis and differential scanning calorimetric (DSC) analysis. When the Nb content is below approximately 28 mass%, the tensile loading-unloading stress-strain curve is similar to that representing the general shape-memory behavior, which occurs due to deformation induced martensitic transformation and its reversion. When the Nb content ranges from approximately 29 mass% to 30 mass%, the tensile loading-unloading curve exhibits superelastic behavior that cannot be explained by deformation- induced martensitic transformation and its reversion. A change in the chemical content of Nb in TNTZ within a very narrow range alters the superelastic behavior of this alloy.