The sinterability of magnesium silicon nitride (MgSiN2) powder with yttrium oxide (Y2O3) addition was examined using the hot-pressing technique (31 MPa and N2 atmosphere) at 1550°C for 90 min; the MgSiN2 powder had been coated with 0-4 mass% of Y2O3 addition by a (urea-based) homogeneous precipitation method. Relative densities of the hot-pressed MgSiN2 compacts (ceramics) with and without Y2O3 addition were ≥99.6% apart for the MgSiN2 ceramic with 4 mass% Y2O3 addition (98.4%). The thermal conductivities of the MgSiN2 ceramics with 0-1 mass% Y2O3 addition were in the range of 20-21 W · m-1 · K-1 whilst the Vickers hardness was 19.7 GPa for the pure MgSiN2 ceramic and decreased slightly with Y2O3 addition. Average fracture toughness values were in the range of 1.2-1.6 MPa · m1/2 with significant trend being noted with regards to the ceramic containing 0.5 mass% of Y2O3. It was concluded that the use of homogeneous precipitation processing resulted in significant advantages regarding the densification, homogeneous microstructure, and fracture toughness despite the amount of Y2O3 addition being as low as 0.5 mass%.