The influence of the hold time of the austempering heat treatment at 280°C on the microstructure and corrosion resistance in NaCl-based media of austempered ductile iron was investigated using X-ray diffraction, micro-hardness measurements, corrosion tests and surface observations. Martensite was only found in the sample which was heat treated for a short period (10 minutes). Corrosion tests revealed that this phase does not play any role in the anodic processes. Numerous small pits were observed in the α-phase which is the precursor sites in all samples (whatever the value of the hold time of the austempering heat treatment).