Hybrid density functional theory (DFT) calculations have been carried out for neutral and radical cation of permethyl-oligogermane, Ge-n(CH3)(2n+2) (n=4-28), to elucidate the electronic structures at ground and low-lying excited states. It was found that a hole is distributed in both the Ge-Ge skeleton (main chain) and methyl group (side chain) in the case of shorter chain-lengths below n = 8, whereas the spin density (hole) in the methyl group becomes significantly smaller in longer chain-lengths (n > 10). The IR-band of radical cation were assigned on the basis of theoretical calculations.