In this study, anodic potentiodynamic polarization techniques were used to study the crevice corrosion behaviour of Nickel alloy 718 (with and without a crevice former) in both aerated and de-aerated solution of 3.5wt% sodium chloride solution. Surface observation of the specimens after each experiment was done with the optical microscope. The results showed that crevice corrosion were initiated at potentials as low as 520mVSCE, while the surface observation on the specimen with a crevice former revealed that the crevice corrosion attack was restricted under the crevice gap and at the border areas of the crevice former but did not occur at the surfaces outside the shielded areas. Conversely, the specimen without a crevice former showed evidence of waterline corrosion. These results can be attributed to the development of differential oxygen concentration in the specimen depending on the exposure of the parts to dissolved oxygen. This study has developed a more comprehensive understanding of the crevice corrosion initiation mechanism and behaviour of Nickel-based Alloy 718 under applied crevice torques, chloride environment and exact potentials, thereby leading to better prevention and control of localized corrosion in this alloy.