In last three decades, RNA molecules have been revealed to play the central roles in many cellular processes. Structural understanding of RNA molecules is essential to interpret their functions, and many biophysical techniques have been adopted for this purpose. NMR spectroscopy is a powerful tool to study structures and dynamics of RNA molecules, and it has been further applied to study tertiary interactions between RNA molecules, RNA-protein, and RNA-small molecules. This short article accounts for the general methods for NMR sample preparations, and also partially covers the resonance assignments of structured RNA molecules.