The submicrostructure of dynamically fatigued Unfilled natural rubber vulcanizates was investigated by using scanning electron microscope (SEM) and atomic force microscope (AFM). AFM photographs showed the sample surface roughness became worse after tensile fatigue and the largest surface undulation was as twice that of the unfatigued sample. SEM photographs showed that many micropores of 10(1)-10(2) mn, a sort of defect, occurred on the cross section of samples after tensile fatigue. The surface roughness became weaker and the size of the micropore was reduced to a few to dozens of nanometers with the addition of antiaging agent N-(1,3-dimethyl butyl butyl)-N'-phenyl-p-phenylene diamine (4020); furthermore, the mechanical properties and dynamic viscoelastic properties in the later period of fatigue changed much. E' decreased greatly and tan 6 increased obviously with the extension of fatigue. It indicated that 4020 was only effective in the early period of tensile fatigue. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 3535-3541, 2010