Electrochemical atomic force microscope (ECAFM) was employed for in situ observation of corrosion of solution annealed and furnace cooled Ti-6Al-4V titanium alloy in 0.5 moll(-1) H2SO4 + 1 moll(-1) HCl mixed solution. A scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS) was also used for microstructure examination and chemical composition analysis. For solution annealed followed by furnace-cooled Ti-6Al-4V titanium alloy, selective corrosion of alpha phase and galvanic effect at alpha/beta interface could be clearly observed at open circuit potential under ECAFM. A higher dissolution rate was also found in alpha phase than beta phase on the bare Ti-6Al-4V titanium alloy. The effect of potential on the corrosion behavior was also explored. Negligible corrosion was found after potentiostatic etching at -0.5 and -0.85 V-pt for 120 min. However, selective dissolution of alpha phase with respect to beta phase occurred when the potential was controlled at -0.9 V-pt. The polarity inversion during potentiostatic etching at -0.9 V-pt was also found and discussed in this study. (C) 2010 Elsevier Ltd. All rights reserved.