Gradient (Ti,Al)N films were prepared on high speed steel (HSS) and Si (111) wafers by using two Ar+ beams to sputter a titanium target and an aluminum target separately, and a third N+ beam to simultaneously bombard the growing film to assist deposition. The effects of the Ti/Al atomic ratio in the films on properties such as hardness, stress, and adhesion strength were investigated systematically. The results indicated that both the hardness and the adhesion of gradient (Ti,Al)N films to steel substrates exhibited ＇＇peak＇＇ type changes with an increase of the Ti/Al atomic ratio, and a maximum hardness of 3780 kgf mm(-2) was reached at a Ti/Al ratio of 5.35. The compressive stress of gradient (Ti,Al)N films increased with increasing Al content in the films. It was found that extreme hardness, high adhesion strength and low stress gradient (Ti,Al)N films can be synthesized on low temperature HSS steel by using the ion beam assisted deposition process. [S0734-211X(99)02702-X].