Scanning Probe Microscope (SPM) such as Scanning Tunneling Microscope (STM) and Atomic Force Microscope (AFM) was shown to be the powerful tool for nano-scale characterization of a fracture surface . AFM was used to study cross sectional profiles and dimensions of fatigue striations in 2017-T351 aluminum alloy. Their widths (SW) and heights (SH) were measured from the cross sectional profiles of three-dimension AFM images. The following results that will be helpful to understand the fatigue crack growth mechanism were obtained. (1) Coincidence of the crack growth rate with the striation width was found down to the growth rate of 10-5 mm/cycle. (2) The relation of SH=0.085(SW)1.2 was obtained. (3) The ratio of the striation height to its width SH/SW did not depend on the stress intensity factor range K and the stress ratio R. (4) Not only the SW but also the SH changed linearly with the crack tip opening displacement (CTOD) when plotted in log-log scale. From these results, the applicability of the AFM to nano-fractography is discussed