Geometries of the bimetallic MO2Gen (n = 9-15) clusters have been investigated systematically with the density functional approach. The relative stabilities and charge-transfer and vibrational properties of these clusters are presented and discussed. The dominant geometries Of MO2Gen (n = 9- 12) clusters can be described as one Mo atom inside a Ge cage and another Mo atom on the surface at smaller sizes with n = 9-12. Interestingly, the stable geometry Of Mo2Ge9 cluster has the framework which is analogous to a recent experimental observation (Goicoechea, J. M.; Sevov, S. C. J. Am Chem. Soc. 2006, 128, 4155). The calculated fragmentation energies and the obtained relative stabilities demonstrate that the remarkable Mo-2-doped Ge-12 is the most stable species of all different sized clusters. The critical size Of Mo-2-encapsulated cagelike germanium clusters appears at n = 15. The largest energy gap and strongest stability Of Mo2Ge12 enable this species to be a unit of multiple metal Mo-doped germanium nanotubes. Vibrational mode analyses Of Mo2Gen clusters demonstrate that the Mo-Mo stretching vibrations are sensitive to the geometries of the germanium frame, and that the point-group symmetry of germanium clusters can vary the Mo-Mo stretching vibration relative to the IR inactive vibration.