Ge nanostructures were fabricated by wet processes based on etching assisted with the catalytic-metal-particles and the electroless-metal-deposition under various conditions. In the etching assisted with catalytic-metal-particles, we used HF+H2O2 solutions after forming Ag particles on the Ge wafer surfaces from an AgNO3 solution. We succeeded in fabrication of porous layers on the Ge substrates and found that the pore sidewall inclination angles with respect to the surfaces can be controlled by the H2O2 concentrations. In the etching assisted with electroless-metal-deposition, we fabricated whisker-like nanostructures and demonstrated that their size and morphology can be varied by changing the AgNO3 concentration, deposition/etching time and the substrate resistivity. We have revealed differences between Ge and Si in the metal-catalyzed etching and pointed out problems in Ge nanowire fabrication via a wet chemical etching.