The GaN:Er thin film has been prepared by direct current (DC) planar magnetron sputtering method. The film was characterized by X-ray diffraction (XRD), Raman, Fourier transform infrared (FTIR) absorption, ultraviolet–visible (UV–vis) and photoluminescence (PL) spectra. XRD and Raman spectrum show the structure of the film is amorphous. FTIR result indicates that the main absorbance of the film is Ga–N stretching vibration. From UV–vis result the optical band gap of the film has been calculated as 3.74eV. Green PL spectrum due to intra-4f transitions of Er 3+ has been observed at room temperature: 2 H 9/2 – 4 I 15/2 (430nm), 2 H 11/2 – 4 I 15/2 (520nm), 4 S 3/2 – 4 I 15/2 (580nm).