Aluminum nitride ceramics are in high demand in electronic industries as substrate materials for applications requiring high thermal conductivity. Sintering and hot pressing are the most common processing methods used to make dense AlN ceramics. However, all methods of AlN sintering involve high temperatures and long times. Therefore, it is an expensive material. Removing oxygen, as a main impurity of aluminum nitride, by a low cost method in order to achieve dense and high thermal conductivity aluminum nitride ceramics has been pursued for many years.  A pressureless infiltration technique at low (650-950°C) temperature was developed to fabricate aluminum nitride-based ceramic matrix composites. The process involves forming a particulate porous compact of non-sintered aluminum nitride and introducing magnesium alloy into the channel network by spontaneous infiltration in a nitrogen atmosphere. Magnesium oxide and spinel phase (MgAl 2 O 4 ) were formed in-situ, when nitrogen gas was used. Densification, thermal properties, and microstructure of the products have been studied. Microstructural, phase, and chemical analysis show that AlN-MgO-MgAl 2 O 4 ceramic composites can be fabricated successfully. Metallic phases were not observed in the samples fabricated at higher than 800°C and electrical conductivity results show that they are insulators. Thermal diffusivity and heat capacity have been measured using nano-flash and differential scanning calorimetry techniques, respectively. Thermal conductivity results are strongly influenced by the residual porosity. Maximum thermal conductivity and density at room temperature were measured to be 95.88 W/m.K and 2.451 g/cm 3 , respectively