Superhard TiB2 thin films were deposited on steel substrates using the radio-frequency magnetron-sputtering technique with a low normalized substrate temperature (0.1≪Ts/Tm≪0.2). The microstructure of these films was observed by a field-emission scanning-electron microscope (FESEM) and grazing-incidence x-ray diffraction (GIXRD), while the composition of films was obtained using Auger electron spectroscopy (AES). It was found that the TiB2 thin films were overstoichiometric and that the diffusion of Ti and B atoms on the substrate surface was greatly improved at a temperature of 350 °C. Moreover, a new dense structure, named the “equiaxed” grain structure, was observed by FESEM at this substrate temperature. GIXRD was carried out at different directions with same the grazing-incidence method and the variation of diffraction intensity of the nonrandom textured grains was confirmed. Combined with FESEM and AES analysis, it is suggested that the equiaxed grain structure was located in zone 2 at the normalized substrate temperature as low as 0.18.