The effects of salt water with 0.5 percent nitric acid on fatigue crack propagation in 2024‐T3 aluminium alloy are studied experimentally. First, the plastic zone size ahead of the crack tip is measured. It is found that the plastic zone size as well as the closure stress in corrosion fatigue is smaller than that in ordinary fatigue. Secondly, the crack propagation rate of corrosion fatigue is much higher than that of ordinary fatigue due to the creation of microcracks ahead of the main crack. Thirdly, the effective stress range governs the crack propagation rate in both ordinary and corrosion fatigue.