The authors present studies on the field emission (FE) mechanism and the FE-induced transformation of individual anatase TiO2 nanowires (NWs). The NWs were synthesized by electrospinning followed by calcination at 500 degrees C which produces polycrystalline anatase nanofibers as determined by Raman spectroscopy and transmission electron microscopy (TEM) characterization. Nanowires of similar to 100 nm in diameter were individually mounted at the apexes of tungsten tips for further physical characterization. The FE experiments were carried out in a TEM which allows the measurement of the FE current while simultaneously observing structural modifications leading to the NW's destruction. For low currents (below 100 nA), we observe reproducible FE Fowler-Nordheim I/V characteristics. Higher currents (up to 1 mu A) can be obtained but sudden destruction of the NW may take place. Our observations show that a thermally-activated transition occurs and leads to rapid re-crystallization phenomena and a variation of the FE characteristics. If not controlled, this transition leads to thermal runaway and sample destruction. The understanding of the destruction phenomena is a key parameter to further improve the FE performance of such nanowire cathodes. (C) 2012 American Vacuum Society. [DOI: 10.1116/1.3668121]