The corrosion behavior of the Ti-33.5Nb-5.7Ta alloy (Ti-Nb-Ta) as a biocompatible beta-type Ti alloy during long-term immersion in simulated body fluid was investigated. Like pure Ti, pitting corrosion did not occur on Ti-Nb-Ta during anodic polarization. Thus, alloying of Ti with Nb and Ta did not change the chloride-ion sensitivity. Metal ion release of Ti, Nb, and Ta was detected after 7-d immersion in the solution; however, the amounts of ions were much smaller than those from Type316L stainless steel. X-ray photoelectron spectroscopy revealed that the fractions of Nb and Ta in the passive layer increased during the immersion while that of Ti decreased. The corrosion rate of Ti-Nb-Ta determined by electrochemical impedance spectroscopy kept decreasing over a period of 15 d while the thickness of the passive layer did not change after 1 d. Thus, the reconstruction of the passive layer of the alloy was proven to be important for metal ion release during long-term implantation in a living body. Thus, Ti-Nb-Ta has sufficient corrosion resistance as a biocompatible beta-type Ti alloy. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.045210jes] All rights reserved.