Mixed films composed of aluminum and aluminum nitride (AlN) were prepared on a silicon substrate by evaporation of aluminum and simultaneous irradiation with a. nitrogen ion beam, ion-beam-assisted deposition, where the nitrogen ion beam current was changed so as to obtain different compositional films. The composition of the films and chemical states of aluminum and nitrogen were analyzed by x-ray photoelectron spectroscopy (XPS). Mechanical properties of the films were characterized by a nano-indentation method. Residual stresses in the films were evaluated by film curvature measured with an optical cantilever system. The XPS studies show that the chemical state of aluminum changes from metallic to nitride with increasing the ion beam current density during synthesis. The nano-indentation tests reveal that the film hardness increases and the recovery behavior changes from plastic to elastic as the ion beam current density increases. From both results, it is proposed that the films change from mainly metallic films of Al to ceramic films of AlN via the mixed states of Al and AIN, The residual stresses were found to be compressive and increase with increasing the ion beam current density. Furthermore, it is found that AN films added by a small amount of Al show the similar hardness to crystalline AlN together with low residual stress.