To evaluate the performance of Zr₆₅Al_7.5Ni₁₀Cu_17.5 amorphous alloy for the biomedical use, the effects of chloride ion, Cl⁻, pH, and dissolved oxygen, DO, on the anodic polarization behavior of the alloy were examined in phosphate buffered solutions. Polarization resistance, R_p, at open-circuit potential, E_open, and pitting potential, E_pit, were determined from the polarization curve. Compositions of passive film generated in a pH-7.5 solution with various concentrations of DO were characterized with X-ray photoelectron spectroscopy. In the solution with pH 7.5, the E_pit decreased with the increase in logarithm of Cl⁻ concentration, [Cl⁻], and showed the highest value with the same DO concentration, [DO], as that in vivo. The concentrations of hydroxide group, [OH⁻], and phosphate ions, [H_xPO₄^(3−x)−], in the passive film were changed with various [DO]s, and the E_pit decreased with the increase in [OH⁻] and [H_xPO₄^(3−x)−]. In the solution with pH 2.2, the E_pit was higher than the E_open with and without DO. Therefore, this alloy may be resistant to the pitting corrosion in vivo.