The ternary nitride MgSiN2 crystallizes in a diamond-like structure with a band gap of 4.8 eV. These characteristics make the compound promising for a variety of applications. Recently we succeeded in preparing fully dense ceramics by sintering at 1550°C. Phase composition, chemical properties and the mechanical properties of the as-prepared ceramics are described. The ceramics are resistant to oxidation in air at least up to 920°C. The thermal conductivity at room temperature has been found to be 20 W/m·K. A considerable improvement of the thermal conductivity is expected when improved processing conditions, well within reach, are realized. A reasonable strength of 270 MPa and a fairly good fracture toughness of about 4.3 MPa·m½ are obtained. A hardness of about 15 GPa and a Young's modulus of 235 GPa have been measured. These new ceramics show that it is still possible to find improved materials as compared to the usual oxide and non-oxide ceramics.