First-principles calculations based on DFT-GGA method have been performed on rubidium adsorption on Si(0�0�1)(2�נ1) surface. The atomic and electronic structures of Si(0�0�1)(2�נ1)-Rb have been calculated and compared with those of Cs adsorption [H.Y. Xiao, X.T. Zu, Y.F. Zhang, L. Yang, J. Chem. Phys. 122 (2005) 174704]. It turns out that the saturation coverage of Rb is one monolayer rather than half a monolayer, similar to that of Cs adsorption. Comparison of Rb on Si(0�0�1)(2�נ1) with Cs adsorption showed that at saturation coverage larger alkali metal (AM) atom leads to stronger AM-AM interaction and weaker AM-Si interaction. However, for low coverage of 0.25 and 0.5�ML the Rb-Si interaction is surprisingly weaker than Cs-Si interaction. Further detailed analysis suggested that this is a consequence of depolarization effect with decreasing AM size below 1�ML coverage. For the saturation coverage, the dispersion curves show that the surface is of semi-conducting character. This result does not support the direct and inverse angle-resolved photoemission investigation where a metallization is observed at saturation coverage.