Synthesis of deuterated and 1 3 C-enriched BEDT-TTF, and the results of 1 3 C NMR (nuclear magnetic resonance) measurement of κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br salt are reported where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene. We synthesized the BEDT-TTF molecule 1 3 C-enriched on only one side of the central carbon sites. By using this molecule, we could avoid the Pake doublet and estimate the density of states from the Knight-shift and the spin-lattice relaxation rate. The reduced mass effect predicted from the specific heat measurement was not observed in the 1 3 C NMR measurement.