In this thesis the synthesis of germanium nanostructures via thermal decomposition in the microwave reactor is presented. The investigation includes the synthesis of germanium elongated nanostructures using different temperature and reaction time conditions, as well as taking different concentrations of the precursors. Tin nanoparticles were used as catalyst seeds for metal-assisted growth of germanium 1D nanostructures. The obtained germanium nanostructures have been characterized via DLS spectroscopy, powder X-ray diffraction, SE and TE microscopies. This work is divided into two main parts. The first part describes the attempt to synthesize crystalline germanium elongated nanostructures with narrow size distribution and uniform shape. The second part is dedicated to the synthesis of tin nanoparticles with narrow size distribution and the diameter under 10 nm that can be later used as metallic catalyst seeds for germanium nanostructures synthesis. The resulting materials are slightly elongated (aspect ratio ca. 1 : 5) crystalline germanium nanostructures with embedded tin nanoparticles with a relatively broad size distribution. The tin nanoparticles obtained by one of the synthetic routes described below have a narrow size distribution of about 2 % and their size varies in 5 - 15 nm range.