Low-temperature growth of c-axis oriented aluminum nitride (AlN) thin films on silicon (Si) substrates by reactive rf magnetron sputtering was investigated. The structural and morphological characterizations determined by x-ray diffraction (XRD) measurement and scanning electron microscopy (SEM) were found to be sensitive to the deposition conditions, such as sputtering pressure, rf power, substrate temperature, and N-2 concentration. A strong AlN (002) preferred orientation perpendicular to the substrate surface was identified at substrate temperatures as low as 150 degrees C by XRD and a densely pebble-like surface texture of c-axis oriented AIN thin films was observed by SEM. The cross-sectional SEM photograph of AIN thin film showed a high degree of alignment of the columnar structure with c-axis preferred orientation. The selected-area diffraction pattern showed that the deposited films exhibited a polycrystalline microstructure.