First-principles density-functional theory and supercell models are employed to study the structural stability and electronic properties of the periodic two-dimensional arrays of identical Nb4 clusters on the Cu(100) surface. The total-energy calculations show that Nb4 clusters with both tetrahedron and quadrangle configurations can be stably absorbed on the Cu(100) surface, which might have important applications. The adsorption of quadrangular Nb4 clusters is shown to be more stable than that of tetrahedral Nb4. The energy barrier for the transition of tetrahedral Nb4 adsorption to the quadrangular one is around 0.94eV/cluster. Electronic structure calculations suggest that adsorption of Nb4 on Cu(100) surface causes significant charge redistributions between the surface Cu layer and the Nb4 adsorbate leading to remarkable changes in the electronic structure of the copper surface.