Tantalum nitride has been found to be a promising material for many applications such as diffusion barrier, wear and corrosion-resistance material, as well as precise and stable resistor in silicon-integrated circuits. In this study, the effect of the amount of tantalum ion, in the plasma, on the electrical property and crystal structure of the tantalum nitride films was investigated. The films were deposited on silicon substrates by a d.c. magnetron sputtering system. The film thickness was measured by an alpha -step profilometer. The sheet resistance was measured by a four-point probe and the X-ray diffraction patterns were used to analyze the crystal structure of the films. The results reveal that resistivity is decreased with increasing optical emission spectrometer (OES) reading. As the OES value is set between 53 and 70%, the variation in the resistivity of tantalum nitride film is small. Decreasing the OES value, the crystal phase will transform from beta -Ta to Ta3N5, and finally to TaN.