In this work, the influence of grain orientation on electrochemical behavior and semiconductor properties, such as donor density, flat-band potential, and diffusivity of point defects (D-0), of the passive films were studied on Nb single crystals with orientations of (100), (110), and (111) in phosphate buffered saline (PBS) and 1 M NaOH solution by cyclic voltammetry, electrochemical impedance spectroscopy, Mott-Schottky analysis, and point defect model. The results shown that the (100) crystal face of Nb exhibits the lowest corrosion rate in both PBS and 1 M NaOH solutions. The Mott-Schottky analysis revealed that the passive film formed on the (100) face has the lowest donor density and the flat-band potential was almost independent of the grain orientations, but decreased with an increase of pH. A different relationship between steady-state current density (j(ss)) and film formation potential was observed in these two solutions and the possible causes were discussed. The diffusivity was calculated based on the point defect model. D-0, of the passive films in PBS solution is in the range of 10-21 to 10-19 cm(2)/s, depends on the grain orientation and film formation potential. In 1 M NaOH solution, D-0 is close to 10-18 cm(2)/s independent of the film formation potential. (C) 2014 Elsevier Ltd. All rights reserved.