Abstract: The effect of molybdate on corrosion inhibition of mild steel add the syner-gistic corrosion inhibition of mild st(?)el with molybdate and nitrite together in deaerated andaerated low hardness water (pH=7) were investigated separately by cyclic voltammetry. The rotating disk electrode (mild steel) was used in these studies. By determinations of pitting potentials, repassive potentials and pitting critical concentrations of Cl-, the resistance to pi-tting corrosion was evaluated. The results indicated that the resistance to pitting corrosion of mild steel inhibited by molybdate is better than by nitrite. Nitrite is favourable to passi-vation; while molybdate is favourable to repassivation. When they are used together, good synergism was-observed, complementing each other in their properties. Studies on cyclic voltammetry of rotating ring-disk eletrode indicated that molybdate improved the repassiveproperty by forming an insoluble molybdate compound.