Partially ordered Fe16N2 thin film with (001) texture is successfully grown on a Ag under layer using a facing target sputtering system. Fe16N2 phase is formed after post-annealing, which is detected by X-ray diffraction (XRD). High saturation magnetization (M s) of Fe16N2 thin films is observed by vibrating sample magnetometry. It is found that Fe16N2 phase can be stable up to 225°C, which is demonstrated by the Fe 16N2 finger print peak (002) in XRD. After heating to 250°C, the Fe16N2 phase decomposes, which leads to low Ms and soft magnetic behavior. To further study Fe 16N2 decomposition, X-ray photoelectron spectroscopy is performed to detect the binding energy of nitrogen atoms. Differences of binding energy corresponding to before and after heat treatment show the variation of nitrogen atom in electronic state with surrounding Fe atoms, indicating nitrogen atomic migration during heat treatment.