High quality GaN nanocrystalline has beenprepared by sol-gel method. The results of X-ray diffraction (XRD), Selected-area electron diffraction (SAED)and High-resolution transmission electron microscopy(HRTEM) measurement indicate that as-prepared sampleis single crystalline GaN with wurtzite structure. Transmission electron microscopy (TEM) displays that the diameters of the grains of GaN nanocrystalline change from30nm to 100nm. X-ray photoelectron spectroscopy (XPS)confirms the formation of the bond between Ga and Nin the sample, and IR spectrum measurement showedE1 (TO) vibrational modes at 570cm-1. Vibrational frequency of GaN small clusters has been calculated usingDensity functional theory (DFT). Using the result, IRspectrum of the sample has been analyzed further.