La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) thin film electrolytes were fabricated on La0.7Sr0.3Cr0.5Mn0.5O3-δ (LSCM) porous anodes by radio-frequency (RF) magnetron sputtering. The formation and microstructure of LSGM thin films were characterized by X-ray diffraction(XRD) and scanning electron microscopy (SEM). The effects of different sputtering conditions, such as Ar gas pressure, substrate temperature and sputtering power, on the performance of LSGM electrolyte film were estimated. Dense LSGM thin film electrolytes with thickness of about 2μm, which are compatible with LSCM-based anodes and without crack, have been successfully fabricated on LSCM-based anode supports by RF magnetron sputtering when sputtering power density is 5.2W·cm-2, Ar gas pressure is 5Pa and substrate temperature is 300°C. It is found that high sputtering power density and high Ar gas pressure, as well as high substrate temperature, are beneficial to deposition of dense electrolyte thin film, close bonding of electrolyte thin film with anode substrate, and formation of large three phase boundaries between anode and electrolyte.