The thermal conductivity () of AlN (2.9 wt. % of Y 2 O 3 ) is studied as a function of the addition of multilayer graphene (from 0 to 10 vol. %). The  values of these composites, fabricated by spark plasma sintering (SPS), are independently analyzed for the two characteristic directions defined by the GNPs orientation within the ceramic matrix; that is to say, perpendicular and parallel to the SPS pressing axis. Conversely to other ceramic/graphene systems, AlN composites experience a reduction of  with the graphene addition for both orientations; actually the decrease of  for the in-plane graphene orientation results rather unusual. This behavior is conveniently reproduced when an interface thermal resistance is introduced in effective media thermal conductivity models. Also remarkable is the change in the electrical properties of AlN becoming an electrical conductor (200 S m -1 ) for graphene contents above 5 vol. %.