The low dielectric constant and thermal expansion coefficient of cordierite are two attractive properties for the material to be used in electronic applications. However, compared to some other materials such as alumina, aluminum nitride (AlN), and beryllium oxide, it has a much lower mechanical strength and thermal conductivity. In the present work, AlN-cordierite composite systems are fabricated using different AlN contents, and the effect of AlN content on the mechanical, thermal, and dielectric properties of the AlN-cordierite system are investigated. It was observed that there exists an optimum AlN content for the mechanical and thermal properties while the dielectric property decreases with an increase of AlN content. An explanation for the observed data trend is offered based on an effective void concept.