Cubic GaN nanoparticles were synthesized directly from reactions of metal Ga and NH4I in liquid ammonia in an autoclave at about 300 degreesC. The influence of the reacting temperature, the kind, and content of mineralizer on the synthesis of pure cubic GaN was studied. Dielectric properties of the GaN nanoparticles were measured on LRC meters under the frequency range of 120 Hz to 10 MHz and the temperature range of 23 to 650 degreesC. It is found that there are three characteristics of the dielectric behavior for the nanoparticles of cubic GaN.