Pseudobinary (Ti1-xAlx)N films were synthesized by a new inductively combined rf-plasma assisted planar magnetron sputtering method. From X-ray diffraction measurement, the deposited (Ti1-xAlx)N films were identified as having the B1 structure up to 50 mol% Al (x = 0.5). In the range from x = 0.6 to x = 0.7, two phases with the B1 and B4 structures were observed. These results suggest that the critical composition for the phase change from B1 to B4 structure is located between 50 mol% Al and 60 mol% Al. The critical composition decided experimentally shows a discrepancy with the theoretically predicted value (65 mol% Al), which may arise from a somewhat high substrate temperature (450 degrees C) in this study. Oxidation resistance increases with increasing the Al content in the (Ti1-xAlx)N films up to 70 mol% Al, irrespective of coexistence of the B1 and B4 phases in the (Ti1-xAlx)N films with x = 0.6 and x = 0.7, while both the hardness and Young's modulus show a maximum value, respectively. Thus, it is indicated that the existence of the (Ti1-xAlx)N films with the B1 structure is quite effective for improving the oxidation resistance, and the appearance of the B4 phase in the pseudobinary nitride films degrades mechanical properties such as the hardness and Young's modulus.