Hydrogenated microcrystalline silicon (μc-Si:H) thin films have attracted many attentions due to the high mobility compared with the amorphous silicon (a-Si) thin films. To fabricate μc-Si:H thin films, plasma-enhance chemical vapor deposition (PECVD) is the most popular method. The disadvantages of PECVD are the high facility cost and using the toxic processing gases such as silane (SiH4). Whereas there is no these disadvantages using radio-frequency (RF) magnetron sputtering to deposit silicon thin films. Unfortunately, the silicon thin films deposited by the regular RF magnetron sputtering are a-Si. In this study, μc-Si:H thin films were fabricated using RF magnetron sputtering with argon and hydrogen as working gas at low substrate temperature (Ts250°C and 350°C). The grain sizes, crystal volume fractions and photosensitivity (ratios of dark conductivities and photo conductivities) of the μc-Si:H thin films which deposited with different hydrogen partial pressures and sputtering powers were analyzed. The results showed that the grain sizes and the crystal volume fractions were increased and the photosensitivity was decreased as the hydrogen partial pressure increased at the sputtering power 200W. The grain size was between 15 to 20 nm and the crystal volume fractions was between 75 to 80% when the hydrogen partial pressure was over 90%.