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, has 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° C. or more and the low-melting point component is exposed on the suture surface entirely along the length direction. 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 not allowing 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.