Many experiments have been made in anin situminiature chamber for x-ray experiments using synchrotron radiation beam during sputtering. We have designed and fabricated a 2 in. circular magnetron sputtering gun for anin situreflectivity experiment. The head diameter of the gun is 6.4 cm, the height is 4.5 cm, and the length of the vacuum tight neck is 11 cm. The permanent magnet is isolated from water for prevention of corrosion. Only one O-ring is used for both insulation and vacuum seal. Therefore, its frame is simple and lightweight, with a volume about 1/5 compared to commercial units. The target holder is not fixed so it can be adjusted for the target thickness. In multi-target sputtering, the distance between target and substrate is closer than commercial equipment so deposition rate and uniformity of the deposited film can be increased. In order to check the performance of the newly sputtering gun,SnO2film on sapphire(0001) is grown, which turns out to be of the epitaxial single domain. ©1998 American Institute of Physics.