Aluminum nitride (AlN) nanopowders have been synthesized by a novel method which combines the hydrothermal and carbothermal techniques. The phase of the nitridation products can be controlled through adjusting the carbon content of precursor by adding different amount of urea (U). The nitridation product synthesized from the precursor (U/Al=2) was comprised of spherical and well-distributed particles with sizes ranging from 50 to 100nm. The nitridation procedure was investigated in detail with TG/DSC, XRD, and TEM measurements. It was found that the core-matrix structured Al2O3/C mixture presents after pyrolysis, favoring the nitridation completed at low temperature, and brings in temperature independency for AlN grain size. Finally, the additive-free AlN ceramic with 99.08% relative density has been achieved by pressureless sintering at 1850 degrees C.