In this work, α-Al2O3 (1–40 vol%) particles (350 nm) were added to a 19.58Li2O·11.10ZrO2·69.32SiO2 (5 µm) glass-ceramic matrix to prepare composites with the purpose of studying the influence of α-Al2O3 on their mechanical, thermal and electrical properties in order to obtain materials for LTCCs applications. The composites, sintered between 800 and 950 °C for 30 min, with relative densities between 85% and 93%, showed zircon and β-spodumene as main crystalline phases. The maximum bending strength (290 MPa) was achieved for composites with 1% α-Al2O3. For composites containing between 1% and 10% α-Al2O3, sintered at 900 °C/30 min, the electrical and thermal conductivities and CTE varied between 3.35 and 1.21×10−10 S/cm, 4.65 and 2.98 W/m K, 9.54 and 3.36×10−6 °C−1, respectively.