Mixed Al+AlN nanoparticles were synthesized by an active plasma-metal reaction method. Mean particle size of the mixed Al+AlN nanoparticles is about 30-50 nm. Defects were found in some AlN particles. Moreover, the AlN ratio and its particle size in mixed Al+AIN nanoparticles obtained in different atmospheres (N2+Ar) increase with increasing N2 particle pressure, and the specific sudece areas of the mixed Al+AlN nanoparticles increase with the AlN ratio. The surface degradation of the Al+AlN exposed to air is estimated by the infrared absorption spectra