The defect properties and atomic configurations in GaN have been comparatively investigated using density functional theory (DFT) and molecular dynamics method with two representative potentials. The DFT calculations show that the relaxation of vacancies is generally small, but the relaxation around antisite defects is large. The N interstitials, starting from any possible configurations, eventually relax into a N+-N< 0 2 11 > split interstitial. In the case of Ga interstitials, the most stable configuration is a Ga octahedral interstitial, but the Ga+-Ga< 0 2 11 > split interstitial can bridge the gap between non-bounded Ga atoms. The formation energies of vacancies and antisite defects obtained using the Stillinger-Weber potential (SW) are in reasonable agreement with those obtained by DFT calculations, whereas the Tersoff-Brenner (TB) potential better describes the behavior of N interstitials.