We present a C-13-based isotope labeling protocol for RNA. Using (6-C-13)pyrimidine phosphoramidite building blocks, site specific labels can be incorporated into a target RNA via chemical oligonucleotide solid-phase synthesis. This labeling scheme is particularly useful for studying milli- to microsecond dynamics via NMR spectroscopy, as an isolated spin system is a crucial prerequisite to apply Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion type experiments. We demonstrate the applicability for the characterization and detection of functional dynamics on various time scales by incorporating the (6-C-13)uridine and -cytidine labels into biologically relevant RNAs. The refolding kinetics of a bistable terminator antiterminator segment involved in the gene regulation process controlled by the preQ, riboswitch class I was investigated. Using C-13 CPMG relaxation dispersion NMR spectroscopy, the milli- to microsecond dynamics of the HIV-1 transactivation response element RNA and the Varkud satellite stem loop V motif was addressed.