Superconducting MgB2 thin films on MgO substrate were fabricated by rf magnetron sputtering. Sputtering was preformed in a 50 mTorr Ar atmosphere at room temperature using sintered MgB2 or pure B and a Mg metal target. Sputtering deposition was followed by in situ annealing at 650 degreesC for 5 min in a high vacuum. The film deposited by a pure B and Mg metal had a superconducting transition temperature of 27 K. On the other hand, sputtering using a sintered target brought on the oxidation of Mg and obstructed the formation of superconducting thin films. (C) 2003 Elsevier Science B.V. All rights reserved.