c-axis-oriented aluminum nitride (AlN) films were successfully prepared on a Y-128° LiNbO3 substrate by rf magnetron sputtering. The dependence between sputtering pressures and the physical structures of the films (crystalline structure and micromorphology) was investigated by x-ray diffraction (XRD) and atomic force microscopy (AFM). The result showed that the higher c-axis-oriented AlN films appeared at lower sputtering pressures and the uneven grain structures existed as multioriented XRD patterns appeared in the high sputtering pressure region (5–9 mTorr). The best orientation and microstructure of the films was prepared at 3 mTorr. © 2001 American Vacuum Society.