Thin films of tantalum nitride (TaN) were deposited on SKD11 tool steel substrate by a D.C. magnetron sputtering system. The influence of the N-2/Ar gas ratio of the inlet gases on the structure, hardness, adhesion and wear resistance was investigated. The X-ray diffraction data showed that TaN deposited at low N-2/Ar gas ratio, tetragonal beta-Ta(330) and hexagonal TaN(101) were observed. Orthorhombic TaN(110) and orthorhombic Ta3N5 were formed with the increase of the N-2/Ar gas ratio. High hardness of the films was observed at the low N-2/Ar gas ratio. The films deposited at N-2/Ar gas ratio of 0.3 showed good adhesion, wear resistance and hardness of Hv(0.05) 1450. The films deposited with etching time of 30 min at 133.32 Pa gave good adhesion. Thickness of the films decreased with applying the bias voltage. As the bias potential was increased, the hardness of the film increased and then decreased. The films with fine dome structure showed good wear resistance. (C) 2004 Elsevier B.V. All rights reserved.