The mechanism of dissolution of Zr in 10 mM HF was investigated using potentiodynamic polarization and electrochemical impedance spectra acquired at various dc potentials. The surface morphological changes in the active and passive regions were studied using atomic force microscopy. The EIS spectra acquired at various dc potentials were modeled using electrical equivalent circuit fitting. A four step mechanism which consists two intermediates and a chemical and electrochemical dissolution steps was used to explain the polarization and EIS results. The model predicts the active-passive transitions in the polarization curve and qualitatively matches the patterns of EIS spectra observed in active and passive regions. The changes of the surface coverage and the dissolution rates with over potential were estimated.