During the synthetic process by chemical vapor synthesis, the influence of temperature and gas flow rate on the size of gallium nitride (GaN) nanoparticles was studied. The mean size of the narrow-dispersed GaN nanoparticles increased as the temperature rose to within a range between 800 and 1100 degrees C. At 700 degrees C, however, GaN nanoparticles were not produced. A faster gas flow resulted in a reduction in the particle size at the ammonia/trimethylgallium ratio of 2400 but not obvious at 1200. These findings can be explained as "coagulation and sintering control regime" and partially as nucleation frequency of GaN nanoparticles.