A numerical study on the dynamic responses of irregular fibers under axial tension is presented in this article. The irregularity was represented by a Sinusoidal shape profile along the fiber axis. The finite element method was used in the simulations and the maximum first principal stress due to the dynamic pulling has been examined. Our numerical results indicate that the first principal stress mainly varies along the longitudinal direction. Its change in radial direction is negligibly small. The maximum first principal stress in an irregular fiber always appears in the narrowest crosssection, which is the weakest link of the fiber. The maximum first principal stress is very sensitive to the change in the irregular amplitude. The very value increases dramatically with the increase in the amplitude of irregularity. The frequency of irregularity has a limited effect on the maximum first principal stress. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113:2561-2568, 2009