Microstructures of titanium wires heated in liquid nitrogen have been made clear by scanning and transmission electron microscopy to investigate the effects of the combustion nitridation of Ti with liquid N 2 . High density N 2 generated from liquid N 2 strongly reacts with Ti wire during heating. Microstructural observations revealed the precipitation of TiN at the surface and the several α phases at the inside of the wire. The heated Ti wire was aligned in order of the TiN thin film, the primary-α phase and the α-acicular phase from the wire surface. The region of the primary-α phase which indicates high solubility of N 2 into Ti was increased by the nitridation with liquid N 2 . An increase in the primary-α phase leads to the accelerated nitridation.