The validity of measuring crack opening displacements by using the high sensitivity Moire interferometry technique was evaluated. The stress intensity factor determination using the crack opening displacements was studied. The data on the crack opening displacement were used to obtain the crack-tip-opening load of a fatigue crack in an 2024 T351 aluminum alloy compact tension specimen. Near-tip and back-face strain gauges as well as a clip-on gauge were employed to record the displacement-load curves used to determine the crack-tip-opening load;The results of the crack-opening load, as determined from these measurements could be separated into two groups: one was the near-tip locally influenced opening load, the other was the crack-face globally influenced opening load. A discussion was given concerning the significance of these results. A residual stress intensity factor was proposed for the fatigue crack specimen.