  Polarizabilities of Ge$_n$ clusters with 2 to 25 atoms are calculated using
coupled-perturbation Hartree-Fock (CPHF) and finite field (FF) method within
density functional theory. The polarizabilities of the Ge$_n$ clusters increase
rapidly in the size range of 2 to 5 atoms and then fluctuate around the bulk
value. The polarizabilities are sensitively dependent on the cluster geometries
and electronic structures. The large HOMO-LUMO gap may lead to the small
polarizability. As compared with the compact structure and diamond structure,
the prolate cluster structure corresponds to a larger polarizability.
