Simple organometallic molecules, especially those with a single ligand, are the desired model systems to investigate the metal-ligand interactions. For such a molecule, a quantitative relationship between the geometry and the electronic configuration would be instructive to test the existing theories and to access more complicated systems as well. As a matter of fact, microwave spectroscopy could be the best approach to address this issue by measuring the pure rotational spectrum of a metal-containing molecule. By doing so, microwave spectroscopy can provide the most reliable bond lengths and bond angles for the molecule based on the rotational constants of a set of isotopologues. On the other hand, from the fine-structure and hyperfine-structure of the spectrum, microwave spectroscopy can also describe the electronic manifold, charge distribution and bonding nature of the molecule in a quantitative way. Fourier transform microwave spectrometers have been the most popular equipment to measure the pure rotational spectrum for three decades owing to the high resolution and super sensitivity. With the advances in digital electronics and the molecular production techniques, hyperfine structures of metal-containing molecules can be easily resolved even for the rare isotopologues in their nature abundance by this type of spectrometers. In this dissertation, molecules bearing metals in a wide range covering both the main group and transition metals were studied. By taking advantage of both the traditional and newly developed molecular production techniques in the gas phase (for example, metal pin-electrodes and discharged assisted laser ablation spectroscopy), we obtained spectra of molecules containing magnesium, aluminum, arsenic, copper and zinc. Our subjects include metal acetylides (MgCCH, AlCCH and CuCCH), metal dicarbides (CCAs), metal cyanides (CuCN, ZnCN) as well as other metal mono-ligand molecules. For the zinc metal, complexes with two simple ligands were also investigated, such as HZnCl and HZnCN. We strongly believe that researchers in different disciplines would benefit from our laboratory studies: theoretical chemists can use our experimental results for calibration; astrophysicists would interpret their telescope observations by matching our precisely measured frequencies; material scientists could find new functional materials by linking the bulky properties of certain materials with our spectroscopic results of the monomers.