A suture to be used in producing a medical instrument provided with a sutured site such as a stent graft, an artificial blood vessel or an artificial heart valve, namely, a suture for sewing a medical instrument. The suture comprises two components, i.e., a high melting-point component and a low-melting point component, the difference between the melting points of components being 30°Cor more and the low-melting point component is exposed on the suture surface entirely along the length direction. The suture is, for example, a multifilament yarn comprising a combination of a high melting-point filament (3) with a low-melting point filament (4) shown in Fig.2 or a composite filament comprising the high melting-point component and the low-melting point component, or a yarn wherein the high melting-point component is coated with the low-melting point component. When a medical material formed of a fabric or a film is sutured or knotted with the suture and then the suture site is heated at such a temperature allowing not the high-melting point component but the low-melting point component alone to melt, the sutured site is fused and fixed. Thus, a knot or a seam, which sustains the fiber shape and strength and never becomes loose, can be formed.
