AIN filler was compared with crystalline silica as a filler for advanced epoxy molding compounds. Properties such as the thermal conductivity, dielectric constant, CTE, flexural strength, elastic modullus and water absorption ratio of water-resistant grade AIN-filled molding compounds according to the contents or size of AIN and the filler size distribution were evaluated. A spiral flow test was also carried out to measure the change in viscosity according to the AIN size distribution for improved fluidity. The properties of EMC that is filled with a 70 vol.% of 12 micron AIN was compared with a crystalline silica-filled EMC. Thermal conductivity was improved by 2.2 times, the dielectric constant was reduced to less than one-half, the flexural strength was improved, and the CTE was also reduced. A binary mixture of an AIN-filled (65 vol.%) EMC showed improved fluidity, thermal conductivity, dielectric constant, flexural strength and water resistance compared to a single-size AIN-filled EMC. The maximum improvement was obtained when the fraction of small particles in the binary mixture of the AIN is 0.2-0.3. The CTE of EMC was decreased by increasing the volume fraction of small particles in the binary mixture of the AIN.