In this study, pulsed dc reactive sputtering of aluminum nitride (AlN) thin films was investigated. The aluminum nitride thin films were deposited on Si (100) using a reactive direct current (DC) unbalanced magnetron sputtering system. The DC reactive sputtering was used in sputtering the aluminum targets in a mixture of argon (Ar) and nitrogen (N2) plasma. Processes of aluminum target sputtering were carried out in an atmosphere of a mixture of Ar and N2. However, pulsed DC reactive sputtering of aluminum targets was carried out at total pressures with N2:Ar ratios from 7:30 to 45:15. In-situ optical emission spectrometry (OES) was applied to obtain the optimal deposition rate and the highest sputtering yield from the effects of flow nitrogen/argon (N2:Ar) ratio and pulse frequency on OES intensity. Thus, we have compared Fourier-transform infrared spectroscopy (FTIR) spectra and X-ray diffraction (XRD) patterns of AlN films deposited on Si (100) by DC reactive sputtering with an Al target in the mixture of Ar and N2. FTIR and XRD investigated the quality of the films and the preferred orientation.