The influence of chloride ions on the passivation of zirconium in phosphoric acid solution has been studied by open circuit potential and impedance measurements. The passivation is found to decrease with increasing chloride concentration. Dissolution of the anodic oxide film in H2SO4 containing different concentrations of chloride ions is also studied. It is found that there is a critical concentration (0.1 N) of chloride ions at which the average rate of dissolution of the oxide film has a maximum value. The oxide film formed in concentrated phosphate solution at pH 2 is the most stable oxide film in H2SO4 solution.