Tantalum nitride thin films were prepared by ion beam assisted deposition technique. Depositions were performed at some different ion-atom arrival rate ratio, and the film properties such as nitrogen composition, crystallinity, and work function were investigated. The relation between ion-atom arrival rate ratio and nitrogen composition was quite similar to that of niobium nitride, which was investigated previously. The structure of the present films was amorphous from X-ray diffraction analysis. The work function slightly decreased with an increase in the nitrogen composition. This result is also similar to that of niobium nitride. The absolute value of the work function was similar to or slightly higher than that of niobium nitride.