Abstract We have fabricated planar type Josephson junctions from MgB 2 thin films by using a Nb thin film as the counter electrode with and without a normal Au barrier layer. The superconducting MgB 2 layer was prepared by diffusion-annealing of B precursor film on a sapphire substrate in Mg vapor. The film surface was mechanically dry-polished with 1/4 μm diamond powder to remove nonsuperconducting residues and subsequently cleaned using argon ion beam. Junction was defined on an area of 4 μm × 4 μm through a 150 nm thick SiO x insulating layer by argon ion milling with photolithography and completed by depositing a normal thin Au layer (0–10 nm) and a 150 nm thick Nb counter electrode. The offset T c was at least 30 K for the MgB 2 electrode and 9 K for the Nb electrode. Current–voltage curves showed typical Josephson transition characteristics. Periodic modulation of the junction critical current under magnetic field was observed in agreement with the standard Fraunhoffer diffraction pattern of a Josephson junction.