Melting behavior of Nylon 6 ultra micro fibers and micro fibers with 0.4～21.0μm diameters has been inbestigated. Two peaks were observed for the melting of the ultra micro fibers. One showed the lower initial melting temperature and the lower central melting temperature with the diameter reduction, and the other showed no variation of the temperatures with the reduction. It was inferred that the melting behavior of the crystal in the surface region of these fibers is definitely different from that of the central region. This surface effect of the fiber on the crystal melting is reported here for the first time
