In order to examine the critical content of AlN for phase change from B1 type to B4 type, Zr-Al-N and Nb-Al-N pseudobinary films were synthesized with an inductively combined rf-plasma assisted magnetron sputtering method. From phase identification of these films by XRD and Raman scattering methods, it is found that phase change from B1 structure to B4 one occurs in the range from 30mol%AlN to 35mol%AlN for Zr-Al-N pseudobinary films and from 62mol%AlN to 70mol%AlN for Nb-Al-N pseudobinary films. The critical AlN content for Zr-Al-N pseudobinary films shows excellent agreement with the value (33mol%AlN) predicted by band parameters. The critical content for Nb-Al-N pseudobinary films is larger than the predicted value (53mol%AlN). It is suggested that the disagreement is attributed to a highly defective structure in Nb-Al-N pseudobinary films.