Abstract: The nearest atomic distance and cohesive energy of cubic and spherical Au nanoparticles were studied by the tight binding molecular dynamics method. The results show that the cubic nanoparticles with 108 and 256 atoms are amorphous in structure while the other nanoparticles are fcc in structure. For the nanoparticles in fcc structure, both the nearest atomic distance and cohesive energy decrease with decreasing particle size for a certain particle shape. And both variation quantities of the nearest atomic distance and cohesive energy of the spherical particles are lower than those of cubic ones. Since the nearest atomic distance is sensitive to the structure variation between amorphous and fcc, the nearest atomic distance can be regarded as a criteria for structure transition. By fitted the simulation results, it is found that the shape effect can lead to 2 96 of the total nearest atomic distance variation and 15 96 of the total cohesive energy variation. The present results on the nearest atomic distance of Au nanoparticles is well consistent with the corresponding experimental ones.