Spontaneous growth of metal-organic frameworks (MOFs) composed of metal ions and 4,4'-bipyridine ligands was successfully demonstrated by molecular dynamics simulations, starting from a random initial placement of the metals and the ligands. The effect of the metal-ligand binding strength upon the MOF self-assembly was investigated. We found that the metal-ligand binding strength should be within a window around the optimum values for the regular MOF growth.