In this work, ZrB 2 -based ultra-high temperature ceramics were fabricated by Direct Ink Writing (DIW) using two different ink formulations containing 10% vol. SiC (ZS10) or 10% vol. MoSi 2 (ZM10) as sintering aids. Rheological tests confirmed shear-thinning and viscoelastic behaviour for both inks, with ZM10 exhibiting higher viscosity and modulus values, indicative of a stronger network structure. During sintering, both compositions underwent homogeneous shrinkage (≈20%) and mass loss (≈8%) due to the removal of organic additives, resulting in defect-free samples. ZM10 achieved higher densification (3.0% porosity) compared to ZS10 (5.5% porosity), confirming the effectiveness of MoSi 2 in promoting liquid-phase sintering. Mechanical characterization showed brittle fracture for both compositions, with ZM10 reaching a flexural strength of ≈270 MPa and ZS10 of ͏ ≈170 MPa. Moreover, oxidation tests showed minimal oxidation for both materials, with oxide scales of 260–360 µm after 30 min exposure in air at 1650 °C. Overall, the results show that DIW combined with pressure-less sintering enables the production of dense, complex-shaped ZrB 2 -based ceramics with tunable mechanical and oxidation properties.