Aluminum nitride (AlN) microparticles treated by silane coupling reagent of -glycidoxy propyl trimethoxy silane (KH-560) are employed to fabricate AlN/epoxy (AlN/EP) composites. Initially, both the flexural and impact strength of the AlN/EP composites increased, but later decreased with excessive addition of AlN. The mechanical properties of the composites are optimal with 5 wt% AlN. The thermal decomposition temperature and the dielectric constant of the composites increased with the addition of AlN. The thermal conductivities of the AlN/EP composites improved with the increasing addition of AlN, and the thermal conductive coefficient is 0.98 W/mK with 70 wt%-treated AlN. For a fixed AlN loading, the surface treatment of AlN by KH-560 exhibits a positive effect on the thermal conductivities and mechanical properties of the composites.