The Er that is rare earth element causes luminescence at 1540 nm, which is a low loss transmission window in silica-based fibers used in optical communications. Moreover, it is known that the temperature quenching of the luminescence of Er becomes smaller with the wide band gap of the host material. We report on the photoluminescence (PL) characteristic and X-ray diffraction (XRD) of AlN:Er thin films which are deposited by RF reactive magnetron co-sputtering method. All the thin films were deposited by RF reactive magnetron co-sputtering method from a 99.999 % Al target and 99.99 % Er chips in a nitrogen gas (99.9998 %) atmosphere. The thin films were achieved with a discharge power of 250 W in a total pressure of 5.0∼10-3 Torr, and the deposition times were one hour. After the deposited, these samples were annealed for 30 minutes in the temperature range from 400 to 900° in a nitrogen gas (99.999 %) atmosphere with an infrared lamp heater. PL spectra of AlN:Er were measured using the 325 nm line of a He-Cd laser at 15 K. Consequently, we observed PL spectra around 1500 nm. The strong luminescence of peak wavelength at 1538 nm is based on the intra-4f emitting centers of Er. We report systematically the experimental results of PL and XRD.