The epitaxial growth process of titanium nitride (TiN) films, formed by implanting nitrogen ions (N-2(+)) with 62 keV into 100-nm-tkick Ti films grown on NaCl substrates held at 250 degrees C, has been studied by transmission electron microscopy, Rutherford backscattering spectrometry, and elastic recoil detection analysis. It has been revealed that the (001)-oriented TiNy is epitaxially grown by N implantation into the as-grown (03.5)-oriented hcp Ti. The TiNy is formed by the transformation of the hcp Ti to (001)-oriented fee Ti during the N implantation, partially inheriting the atomic arrangement of the square and/or the octahedron of the hcp Ti, as well as the occupation of ill in octahedral sites of the fee Ti. Strain due to the expansion of the lattice and/or the volume of hcp Ti by N implantation can be considered as one of the driving forces for the hcp-fce transformation of the Ti lattice. The nitriding mechanism of epitaxial Ti thin films is discussed.