Structural changes during the creep process of ultrahigh-strength polyethylene fiber (UHSPE) were investigated using X-ray and the solid-state NMR techniques. As the creep strain increases, the quantity of the amorphous phase area estimated by the C-13-NMR method increases until the final creep rupture. On the other hand, the amorphous quantity estimated by the X-ray method does not change noticeably. To explain this contrast, we proposed a new model that illustrates how the defects such as chain ends incorporated into the crystalline phase are excluded from the crystallite and agglomerate to generate a new amorphous area, which has a size hardly detected by the X-ray method. These small amorphous areas are considered to cause a decrease in the tensile strength and the successive final creep rupture.