In this paper, an in-situ scanning electron microscope (SEM) fatigue testing was performed to measure the crack growth kinetics and the corresponding crack tip opening displacement (CTOD) at the any small time instant during the constant cyclic tensile loading. The objective of the experimental study is to verify the hypotheses of a small time scale fatigue crack growth model. During the testing, one loading cycle is divided into a certain number of steps. Images are taken at each step around the crack tip region. Imaging analysis is used to quantify the crack growth kinetics and crack tip deformation behavior at any time instant in a loading cycle. Crack closure phenomenon is observed during the crack growth process. It is also observed that crack growth is not uniformly distributed within a loading cycle and only happens during a small portion of loading path.