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 °C which produces polycrystalline anatase nanofibers as determined by Raman spectroscopy and transmission electron microscopy (TEM) characterization. Nanowires of ∼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 μA) 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.